Looking for a party theme that is easy to put together? Throw a Tiki Party! You can go as simple or as overboard as you like. It's relaxed, casual, a bit kitchy, and decorations are easy to find or make. As for food and drink? Asian inspired finger foods, lots of tropical fruit and juices, and rum (or just stick with the juice.. up to you).
Consider Tiki as a sort of polynesian, sort of carribean, mish-mash of Island culture. Lots of flowers, lots of palm trees, tropical drinks and "exotic foods". And of course... you need a Tiki god.
Plus, your guests can choose to go nuts with their look (hats made of palm fronds are a fine example) ... or show up wearing a simple aloha sirt or sun dress. (Even the guy who never wants to go along with "theme parties" can scrounge up a pair of shorts).
A Tiki Party is a great theme for a Backyard Party in the Summertime (but imagine the fun you could have celebrating tiki in the winter!)
I have lots of great ideas for throwing a Tiki Party... use as many or as few as you like... You WILL have a great time.