I carry a multi tool, a couple of co2 cartridges, a tube, and some tire levers either in my pocket of my jersey; or more usually in my camelback since I don't use water bottles when I mountain bike. They get too dirty and are too hard to drink from when I am bouncing around on a bunch of rocky trails.

You can use a small saddle pack; but I don't ever put the tubes in those because sooner or later the tube will get rubbed by the zipper and be damaged.