For my ds, the best things to keep him occupied on his own are sets that he can use to make things. Mega blocks, wooden blocks, train set, a set of PVC pipes and joints, etc. For some kids, crayons and coloring book would be perfect. A baby doll was perfect for my dd1--she likes to put the doll in a mini infant seat, a doll sling, a stroller, give it a paci, read it books, etc. while I'm taking care of the real baby.
Computer games have also been a lifesaver for me. My 2 older kids both learned to mouse before age 2 and love to play at starfall.com and some little CD Rom games we have.
I like to give "becoming an older sibling" books as gifts--those could go in a basket as well. My kids don't sit and look at books on their own for longer than a minute or two but I like to read to them while I'm nursing. I really like A Baby Sister for Frances by Russell Hoban, the Little Critter new baby book, the Bearenstein Bears new baby book, to name a few.
