the suggestion to buy a few bigger items in larger sizes - especially things like the onesies and sleepers is an excellent idea. The babies usually grow SO FAST!
Also, last time I looked, the onesies came in short sleeves and long sleeves.
But it's been a while since I've looked.
For a baby shower gift, I would usually get a small laundry basket, some Dreft, some disposable diapers and wipes - and then depending on how much more money I wanted to spend, some more diapers in a larger size, and baby clothes hangers. Then I put the stuff in a large trash bag and tied it with pretty ribbons.
Usually didn't get much in the line of "oh, how cute" comments at the shower, but I did get comments later from the Mom on how useful this was