About 20-30 people bike to where I work. What equipment/supplies should we have on hand? I work in San Francisco, and I'd estimate about 20-30 people bike to where I work. We mostly have a mix of road bikes and hybrids with a couple commuter bikes and mountain bikes too.  Currently, the only equipment in our bike cage is a locking entry door, a double-decker bike rack similar to this one, and a single floor pump.

I was thinking that we could start with some basic toolkit or repair kit, spare batteries for lights, loaner headlights and tail lights, and maybe a couple loaner helmets so people don't have an excuse to ride without helmets.

What else should we stock?  Are there premade kits for a situation like this?
I'd maybe ask the cyclists themselves - maybe ask them to bring useful spares and have an amount of petty cash on hand to reimburse them. They might be able to bring in old lights (let's face it many of us always leap to the newest kit and have drawers full of old kit lying around). 

The basic tool set should include tyre levers, an adjustable spanner/wrench or combination bike tool, Allan keys (hex wrench). 

If you're prepared to keep things topped up with consumables as well, that would be great - but you'll be forever replacing the inner tubes, but while you might need a mix of sizes, starting just with a few 700x25c would work. 

I'm not convinced about spare helmets - apart from the whole obligated helmet wearing debate - you might be opening yourself up for liability if someone got badly injured in an accident while wearing one of the loaner items. 

Many lights these days are rechargeable themselves, either through USB or directly to mains, so making sure that there are charging sockets and a charged USB hub could be good, maybe a battery charger would encourage people to switch to that style of battery.