I am planning on going on my first trail ride with a group this weekend. I still don't have any tools with me and will be buying them on Saturday. What compact tools do I need to buy to carry on my ride in order to survive on the trails.

Well first check what drivers you need, maybe for brake tuning and if you need any wrenches...I do as I don't QR my seat.

Metric hex keys.
Multi-tool.
Tools to take off tires (I use 2 old QR levers).
Say 2 new tubes, a patch kit, air source.
Zip ties (good for tie off\get home repairs).

Take a small med kit too, bandaids, sterilizer, tensor bandage.

pretty much what jeff says. I would say that you could probably get by with only 1 spare tube, and if the trails aren't super long, you could leave the med kit in the car. (that's what I normally do)

Get a good multi Tool such as Park's MTB3; you don't need to carry tire irons while MTB riding with this tool-BUT you will with a road bike because the tire irons are too wide for road tires. I have the original version of this tool and it works great, in fact I turned to it when at home dinkin with the bike because it's easier to get to since it's already on the bike.

You need a patch kit; I prefer the glueless because they work and their faster to use with no dry glue tube surprises. By the way, glueless patches ARE NOT temporary patches as some argue; I have a 3 year old tube in a road tire with 2 glueless patches and their still working, I have a MTB tube with 5 and still holding air.

Also carry a boot patch in case of a large tire hole.

I would recommend carry a spare tire-BUT on a MTB that's impractical due to the size of MTB tires. I carry a spare for my road bike but it folds up into the seatbag, on my mtb I can't do that. But I actually ride in more remote places and further from home on the road bike then I do on my mtb so a spare tire is more important on the road.

But carry a spare tube.

Get a cheap folding pair of pliers Leatherman type of tool; I got mine from Target for $12.

Of course don't forget a pump! I use mini for both road and mtb, but with a mtb a mini is easier to use because the tire pressures are lower.

Zip ties I'm not sure if I would bother, but you could carry a small roll of duct tape.

Some people I know carry a fiber spoke or two in case a spoke breaks but I never had a problem with that so I don't.

Also some people carry a spare chain link, but again I don't since I never broke a chain. Also if you chain did break you can reassemble the chain with one less link which means you may not be able to use your largest or smallest gear but the middle gears will work just fine.

My last 3 suggestions are probably just a waste of time and bag space, but only you can decide that based on experiences you might incur.

It's not exactly a "tool," but put some kind of energy bar in the seat bag in case you need a boost. And the wrapper can serve as an eemergency tire boot.

Also, I generally only carry two tubes if I'm doing > 50 miles. Instead, I carry one extra tube and a patch repair kit. I wrap a little electrical tape around one of my wrenches. You could do the same with duct tape.

Edited to correct type-o: I originally said, "I generally only carry two tubes if I'm doing > 50 mph." I wish.

cell phone. Can call someone in a pinch.

good post froze! I'll add that like you, I haven't had a problem with needing spare spokes. Even when I had a set of wheels with carbon spokes for my MTB and would routinely break a couple on the rear wheel while riding, I could always finish the ride (albeit a little more slowly) and just get it fixed afterwards.

I do carry a MTB tube when I ride, but I use a Camelbak so the space isn't really an issue for me.

Oh, (for the original poster) and don't forget to carry a chain tool to fix that broken chain (unless it's included with the multi-tool you get.

I second (third?) the spoke idea. On long rides, I carry an extra spoke. But I don't bother if I'm riding where I can get help. I've only broken a spoke once, and that was in town. I just used the bus fare I always carry to get to work and home again (thank you COTA for the bus bike racks!). At a minimum, you should make sure you have a spoke wrench. Most good multi-tools have one. In a pinch, you can tighten spokes on either side of a broken one.

Or carry a Sram PowerLink or two to do the repair. I guess you might have to get a broken piece off first.