i would say,..it depend on what rig you're riding (me,SS all the time/all the way) and jim riding geared.50% on geared is not much, you can go more than that,and as jim stated before don't burn it too earlier you want to keep it at your steady fitnes level don't go beyond that unless you're comfortable with it.it also dictated by the terrain itself (hilly or flats) if you're riding long enough long distance rides you'll mastering one or more thing...about how to rides longer and stronger and heck.. you'll even have some fuel left when you done.
what to bring and whatnot..
it takes times and some basic knowledge to get thing done properly,not too much and not less either.and also you'll will learn proper way how to fuel up before,during and after rides.
jim,OTOH is the master of endurance, of course he don't need pack.😀
me, personally within distance 40 t0 70 mile i don't carry pack (only tools,some gels/bars and bottle water and i'm riding with my jeans plenty of room for wallet,cell and camera) and if i hungry a visit to a nearby resto is a must...but for longer than that, esp in new teritory i would considered bringing pack(beside it's good for your shoulder and your back 🙂, of course unless person with back problem i wouldn't recommend pack for long haul)
just my one cents!