I've been using an LL Bean open tote in the large size, I think it's 35L.
It's worked just fine, I can fit my shoes, helmet gear bag, kit, tools and misc junk with no problem.
The one thing I don't like about it is that I have to carry it. For mountain biking and road rides it's no problem, but at the track it generally means at least 2 trips to get my stuff to the infield.
I was going to build a wagon, but decided against that approach. I've helped enough guys carry theirs over the bridge at T-Town to rule it out.
I don't usually take that much to the infield; bag, bike, rollers, wheels and a water jug. This season I'll replace the bag with a back pack and see if I can do it in one trip.
PI