Plan gift giving in advance, This will give you time to think of an appropriate gift and find it at a good price.
The last thing you want to be doing is stopping at StuffMart on the way to a birthday party and paying full price for some random gift.
When we see a great deal on a gift item (Amazon is great for this, plus you save on gas and no sales tax) we buy a few extras and put them away. With all the kids we have, they get invited to a lot of birthday parties.
This routine of ours also comes in handy for last minute parties or one's that you have forgotten about.