I've experienced a few flights with little ones - it's amazing how much difference a month or two makes at this point. So Izzy will be 8 months - probably not walking quite yet, but she won't sleep the whole time, like a little one. (International flights with a three week old or a six week old are surprisingly relaxing - with an 18 month old, not so much.) Depending on the time of the flight, try to bring whichever foods she'd normally be eating at that time. If you've started her on solids, bring along (on the plane) a couple of little jars of the simplest thing she's eating, and maybe even a little tub with some dry cereal in it to which you can add water or formula as needed. If you can find those tiny little ziplok boxes, those would be the perfect size/weight.
Getting through the airport, you can use your stroller right up to the gate, and then, if you have a sling or a baby carrier, that would be helpful for keeping your hands free. Then when you get off the plane, you'll have the stroller right from the plane. This can be a pain if there are stairs at the gate, but otherwise it's usually pretty convenient.
I've always nursed my kids when they were that age, so I didn't have to muck about with bottles, but you'll definitely want to let her have one during take-off and landing to deal with pressure. If she's asleep during landing, she'll probably be alright most of the way, but may wake up just near the end, so you might want to have a bottle made up before they put on the fasten seat belt sign!
I have a diaper bag that I use as a carry on - it's big enough for a week's worth of diapers, but I usually only put in what I'll need for the duration of traveling (my rule of thumb is one diaper for every hour from when I leave the house til when the grocery store opens in wherever I'm going). That way, if my checked bag doesn't make it, I'll have enough to get through the first night! I've never run out of diapers yet, but did have a close call on our recent train trip across the US - I hadn't planned on a 12 hour delay...
However, as Miss Chick said, don't take the whole diaper bag into the bathroom - just grab a diaper and the wipes and be done with it. The toilets usually have little flip-down changing tables over the toilet, they're not elegant, but serve the purpose. Some smaller/older planes may not have tables in every stall, you might want to check with the attendants first.
If you have one of those little "travel" wipes holders, they're seldom big enough! I usually get one of the 40 wipes packs in the soft plastic bags - the hard cases usually only hold about 20, which isn't quite enough for me. Of course, I have four other pairs of hands to clean, so that might be part of the problem...
Back to the diaper bag. I always pack a change of underclothes for me, and a clean shirt or even a sundress if I can fit it, because, well, you know. Also, a minimum of two changes for the baby. A pajama and a sundress would get you through even if your bags didn't make it. If you still have room, throw in another onesie. You'll never regret having a change of clothes!
Which brings me to the ultimate baby item ever, the sarong. It's better than an AmEx card, so you know you need one. They are so lightweight and compact, hand wash and dry quickly, which means you'll have it handy when you need - a blanket on the plane, or a light layer in an air-conditioned building, a burp cloth, a towel after swimming, a change of clothes (for mom or baby), a sun shade, an umbrella, a windscreen, a diaper changing pad, beach blanket, picnic tablecloth, high chair liner, sling (I was thinking to hold sleeping baby, but I suppose for medical purposes, too), a curtain, something to play peek-a-boo with... there's no end to this list.
Fun things to do on the plane: sleep. Other things to do on the plane: at this age, not much. If you plan to hold her as a lap child, they'll give you an extra little seat belt that attaches to yours. The biggest hassle travelling alone with a lap infant is going to the bathroom on the plane. Try to go just before boarding, while the baby's still in her stroller. If you're buying her a seat, she'll be in a car seat, so you'll be able to leave her briefly - but be sure to put yourself closer to the aisle so you can get out easily! In my experience, the flight attendants love to hold babies, and are quite willing to help you out if you need to use the loo.
I'd bring along some quiet toys, maybe a teething ring, and something with which you can attch the toys to your seatbelt, arm or something so you don't spend the entie flight retrieving toys from under the seat, or apologizing to neighbours who've just been whacked in the head with a sloppy toy.
Xavi is 8 months now, and I get a lot of mileage out of variations on peekaboo, and one of those crinkly, rattly, colourful, textured toys can provide some interest too. You know best what she likes to play with. But I usually only take one or two toys along, and make use of whatever else happens to be around. An empty water bottle, lid securely fastened, kept my little one entertained, on and off, for three days on the train.
As far as packing, four swimsuits? That might be enough.
Hot climates are so easy. Onesies (she can sleep in them), a couple of sweet little sundresses - I have observed that crying babies that are adorably dressed are tolerated more than crying babies in grubby clothes. It's not fair, but there it is - a terrytowel cover-up is a good idea for the beach, both to warm up after playing in the water and also to protect her from the sun and wind. She'll also need a big, floppy, tie-on hat. You can probably find something fabulous there, but be sure it ties on so you don't spend your holiday playing izzy-takes-it-off-again-mummy-puts-it-on-again! She's old enough that you can use sunscreen, but I still try to find the very most gentle kind available - high spf, low nasty chemicals. We've lived in cold, wet places for so long now, I haven't a clue which brands are out there anymore! If you can get a beach cover up, you don't have to be as vigilant with the sunscreen. If she's starting to stand a bit, you might want to bring along some sandals, and if she's crawling, you might bring some lightweight leggings to protect her little knees and shins on potentially rough surfaces.
One thing that I didn't expect when first traveling with my eldest, is the amount of attention you draw. Sometimes this is positive, sometimes not so much. People, especially those of grandparent-y age, tend to be quite solicitous of moms traveling with babies, and I've noticed a big difference whether I was traveling with or without my husband. With my husband I'll get smiles and the occasional remark, without my husband, people do not hesitate to comment, offer to help, occasionally more than you would like. If you want to put anyone off, here's a handy remark that'll generally work - "Oh, excuse me, I think her diaper may need changing." I used that just today, actually. Works a treat. And it's technically not even a lie, as baby diapers pretty much always, may need changing.
We have also found that in most places outside north america and northern europe, people love to touch, snuggle, hug, kiss, pet, squeeze and generally love on babies. And in our experience, blue eyes and fair hair, in places where these are less common, are particular draws. Don't know if that applies to your little one, but it's good to know in advance. A friend of ours had a blond son who, when they lived in Korea, wore a hat everywhere, because he was uncomfortable with people touching his hair everywhere he went. When we were in Korea, people loved to touch my daughter's blonde hair, but it didn't bother her. If your baby is comfortable with lots of different people (my little one will go to strangers on the bus, my son wouldn't at all), all the attention will be fine, but if she is less comfortable, it's helpful to know in advance that she will likely get more attention than she wants, and it may make her tired, cranky or clingier than usual. If she's getting more attention than she or you are comfortable with, carrying her in your arms, a sling or other baby carrier will usually make her feel better, and people are somewhat less likely to come up and touch babies when they have to get right up close with an adult at the same time. Not a guarantee - I had a woman drag her husband over to peer over a blanket at my NURSING baby when I was leaving the hospital with her in Germany. She wanted him to see her little face. Fortunately it was Germany, and nobody has any privacy issues. Well, except ME!
Maybe the biggest difference now that you're traveling with a baby is that everything will take longer. Yes, you have to factor in extra time for emergency diaper changes, feedings and what not, but you can also anticipate that people will stop you to admire the baby and chat both about yours and their children. This can be an incredible opening into a culture (I know you're well versed with DR, I mean broadly speaking) and a tremendous opportunity to really connect with people.
Sometimes, it's just a pain. But if you anticipate it, you probably won't miss your bus, plane, whatever!
Have a wonderful trip, and enjoy your break with your lovely little girl!