Present for a 4 yr old boy?

[Yeni]

I need to get a present to take to a birthday party for a 4 yr old boy for around £10. Please inspire me! I don't know what he likes or what he has already. In fact I don't know much about 4 yr old boys at all!

A small tub of lego ... think they do one for £9.99 would probably go down well .. or playmobil. Books or sticker books are good too.

Would second the lego suggestion (though not one of the models they put together - IME they are too fiddly for a 4 year old).

Thanks - I'd forgotten all about lego!

Playmobil, Lego, Meccano (the age 4+ plastic stuf, not the more fiddly 8+ stuff), K'nex. Does he have a wooden train set? If so, track/accessories for that, e.g. a bridge or tunnel or points.