What should I do for my friend's birthday... 1 month late?

One of my good friends' birthday was about 3 1/2 weeks ago, and I still don't have his present. He hasn't said anything about it but I know that it will hurt his feelings if I don't do something eventually... But I'm also pretty embared not having his present yet and not really having a good excuse, other than just being busy and being forgetful lol :). What should I do? Gift card? One of those stupid "belated" birthday cards? Something really expensive to buy his friendship? Lol just kidding about that one. I only have about $20 to spend and he just turned 15... what should I do?