Go Light!
Most of my riding back in the day was of this type- before sus too!
Its much easier if you have a few friends with you to spread the load- a rack helps but i never took panniers.
A typical ride would be friday evening on the train to the lakes or North Yorks Moors and back late Sunday night- 60-70 miles a day.
Choose a fast rolling tyre because you will have plenty of tarmac no doubt- Specialized crossroad IIs were our fave back in the day.
Medium size rucksack with a spare pair of undercrackers and socks and a lightweight fleece and a hat for the evenings (one of the lads always took an old pair of overalls for sitting around the fire in and its amazing how warm and light they were and packed down really small!) thats all you need clothes wise. Get a decent lightweight sleeping bag and a roll up mat and an old 2 man tent flysheet to make a shelter (we're talking wild camping with a fire here so no need for a tent), cut your toothbrush in half, get a cheap headtorch, a disposable lighter, some toilet roll and a bottle opener and thats all you need.
We would pitch up just outside a village out of the way, stash our bags, wash in a stream and ride down to a pub and feed and water ourselves (don't forget to get a few bottles as a take out at the end of play). Get back, light the fire and sit around fettling the bikes until the early hours whilst shooting the crap.
Spares wise, just take a tube, a repair kit, multi-tool and a few cables (spread this lot out amongst your buddies)- you'll find that will get you out of the shit (this is where old school rigid steel bikes really shine- nothing much to go wrong.
Other tips- bottle cages and bottles, leave the hydration pack at home- keep the weight on the bike and make sure you take some string, zip ties and gaffer take- three of the most useful things in the world.
Always make sure you leave your camp just as you found it, apart from that just go for it- it's such a liberating thing to do and even the weather won't spoil it if you have the right mindset. Waking up out in the woods is one of lifes great pleasures. If the weather turns nasty- improvise, we once spent a night in the toilets in Dalby Forest- they had just been cleaned and were quite comfortable and had the benefit of lighting. Knowing a little camp craft won't go amiss, lighting a fire when its been raining all day isn't easy.
Planning to do more of this myself next year when things settle down a bit at home- might see you out there someday
Oh- Almost forgot, put your clothes and sleeping bag in two separate heavy duty bin liners to keep them dry for those waist deep river crossings!
Have fun and let us know how you got on dude.