Vacation - oh yes and oh no.

Awesome that you're going to Hawaii - enjoy! Tell your sister, if she doesn't already know, that you're simply trying to eat more healthily, not necessarily that you're aiming to lose weight, because sometimes that puts people on the spot about what kind of food THEY'RE preparing and eating. Also, making a big deal about dieting/what you can or can't eat puts people on the spot as well. Best to be discreet. Offer to help out with food prep - I'm sure she'll appreciate that, UNLESS, she's a complete kitchen control freak LOL! In general, when you see something particularly healthy, make oohs and ahs about it and say how delicious this looks! This should be easy with all the Hawaiian fruits, and festive fresh foods in a good restaurant. Depending on what island you're going to, a trip to a local growers' market would be fun, and garner some great healthy foods, and get you in touch with the local flavor too - always a plus. I know my husband and I LIVED off of what we got twice weekly at the Hilo Farmers' market on the Big Island.
When you eat out, try to make good choices. Avoid the deep-fried, heavily-sauced stuff, and quietly order leaner items if at all possible, In Hawaii, depending on the restaurant, there should be good seafood on the menu, something with vegetables, grilled items, and think of all those fresh fruits! If there's a local high-calorie treat you simply must have, go ahead and have it, just not a huge serving. A very popular dish throughout the islands among locals is the plate lunch. Usually this is a nutritional disaster with both 2 scoops of white rice and a scoop of macaroni salad along with the meat. Some places, however will let you make substitutions like brown rice and or salad instead of all the white carbs. Finally when eating out, you don't have to eat the whole thing right then and there - doggy bags exist for a good reason:)
Also, that 2-week break from strict dieting(within reason) is good - that temporary increase in calories is sometimes good for a change, like taking a short training break. One will come back stronger and more able, and one will be eager to hop back on one's dietary program once again. If you're able to just maintain your weight while travelling, that's excellent! Anyhow, enjoy the trip!