It depends on how old the child is:
My 10 year old, I usually pack, the indispensible GameBoy, CD player and CD's (We made a CD last year at AK with all our favorite Disney songs on it, my kids just LOVE it), Markers or colored pencils and paper.
My 2, 5 & 6 year olds, I usually pack: Disney coloring books, stickers, colorform books, travel size magna doodle, juice boxes, animal crackers and bananas or apples.
Hope this helps!