Gift cards are definitely a good option - not too "fun" to give (they don't feel very personalized I guess), but very nice to receive. My 3 year old DS got one for his Bday and had a BLAST picking out what he could get with it (a good lesson in money, too, since he only had X amt of dollars to spend).
If you still want to make something, the pillowcases and purse/wallet combos are a good idea. Maybe some beanbags for the boys? I'm sure you could find tons of game ideas online to print out to go with them.