Ah, the family get-together. Fun? Sure... but you might also be driven insane. Why not pack some of these things in order to stop it from happening?
-A book
-Hand-held video games (like a gameboy or something)
-Candy/gum
-A puzzle
-A favourite stuffie (stuffed animal) or two 
-A board game
-Drawing materials (paper, pencils, crayons, etc.)
-Entertaining toys (a ball, chinese finger traps, yoyo, magnetic building sets, etc.)
-Writing stuff
-Music player (walkman, MP3player, etc.)
-Hand-held virtual pet games
-Games (jacks, dominoes, etc.)
-A deck of cards
-Macrame (string-tying for friendship bracelets, keychains, etc. AKA finger knitting)
-Cat's Cradle
-Snacks
-Stories and jokes to tell
-Funny poetry to read
-A camera - try to get the funniest photos you can!
-A video camera
-Crafts
Here are some other things to try:
-Ask if you can bring a friend or even a small pet
-Ask wacky questions ("If you woke up one day in your favourite TV show, what's the first thing you would do?") to start a conversation
-Pull out photo albums and look through old pictures with people
-Play some fun-for-all type games that people can join at any point. If you have a lot of fun (and make a lot of noise), you'll soon have everyone involved!
-Ask your parents about family members' interests before hand - it makes it easier to start a conversation later