The three-ounces and under rule for flying is an inconvenience if you are trying to travel with a carry-on bag. But you can get around it pretty easily with small containers, travel-sized toiletries, or innovative products like non-liquid travel sheets.
There's one item that is especially problematic though: sunscreen. Three ounces of conventional sunscreen isn't going to last you very long if you're vacationing in the tropics. You could wait and buy it there, but you'll pay twice as much.
So, when I was going to Roatan Island on Delta--which only flies there one day a week--I brought along this three-ounce spray sunscreen from CVS. I was skeptical about these spray sunscreens when they first came out, but if you really rub them in evenly, they seem to work just fine. The real benefit for travelers though is you can get a lot more use out of three ounces of spray than you get from that amount of regular sunscreen lotion.
This sunscreen comes in a strong aluminum canister and has an SPF of 30. (And it's actually more squat than the bottle pictured here.) In my tests in the blazing sun on a beach, it performed well and didn't feel as gunky as the usual stuff. I used it for five days and still had enough left that I brought it home. The three-ounce spray sunscreen from CVS retails for $5, but is often on sale for less.