Supplies. Find out what kind of tubes he uses and buy him a few of those. Find out what types of socks he likes to wear and buy some of those. Does he have a CO2 air system? If not, buy him one along with some spare cartridges. If yes, buy him so cartridges. Look at his gloves - are they beat up? Could he use a new pair?

A lot of this stuff is slightly boring, but it's stuff we need...