Working support for a charity ride is the bike mechanic equivalent of camping. You do all of the things you's normally do in a day, but simpler and outside. It can require some creative problem solving. You never realize how often you rely on a bench vise to do your job, until you don't have access to one.
I'm stocking up with tubes, tires, extra cables, a chain or two, a handful of misc. bolts and brake pads.
There's a good chance I'll go through a bunch of tubes, and a tire or two. If you're headed out for any charity or organized rides this summer you clearly don't need to be this well stocked. I'd recommend a tube, tire levers, an inflation device (my faves here and here), and a multi tool. That should have you pretty well covered.
The shop will be open for regular hours- I (Emily) won't be here, but Erich will be. You know Erich? Nice guy, glasses, kinda beardy, knows a lot about bikes. If you don't know him- stop by on Saturday and say 'hi'.