35 litres is more than enough for an overnight bag, although saying that, I find it much harder now to stay below that volume than when I was a skint schoolkid.
When I was 14, a couple of mates and myself spent almost a week wandering around Ennerdale and Buttermere, carrying everything in our 50 litre frame rucsacs, which we thought, at the time, were the height of technology. We had plastic sheets for tarps ( that we'd nicked off a building especially ), sleeping bags and orange plastic bivvy bags for when things got really wet ( which, as it turned out, was four days out of six ). Most of our food was tinned, but it turned out that hot dogs and beans are good for morale, and can be eaten cold if needs be. To save our two Camping Gaz Bluet cartridges, we cooked over a fire as often as possible using our ex army mess tins, although the wood was so wet that most of the time we had to use the stove to start the fire, and we realised early on that mess tins are probably the least efficient pans in the world.
On that trip, the major navigational gaff that we made was mistaking Kirkfell for Great Gable; we only realised that we were on the wrong mountain when the cloud lifted for about two minutes and we realised that pillar was a bit close.
The quote of the trip though, was on the last day. We were sat on the shores of Crummock Water brewing up and having a snack before our walk back to the bus stop in Cockermouth. A large group of walkers passed us, wearing gear that we'd only ever seen in shop windows in Keswick. One of the kids in the group stopped and stared at us, and then uttered the immortal line: "Look mummy, nomads."
Cheers, Michael.