I buy in bulk in advance. I currently have two in school and they both get invited to parties of the opposite sex as well as their own sex so I buy gifts in bulk that can be used for either sex.

Basically if I see something super cheap or on clearance I will buy a couple of them and put them in my presents drawer. I do this either at the shops or using websites like catch of the day - they sometimes have really good book sales and I have gotten some great cheap ones off that.

I do aim for around $15 per child but am happy to spend over if it is one of their closer friends.