Panniers are the traditional - and still the best - way of carrying a lot of weight on a bike. If you're touring and camping, there really isn't a viable alternative. The best set up is a pair of large (60 litre or so) panniers on a good quality rear rack combined with a pair of smaller (20 litre or so) ones on a low-rider type rack on either side of the front wheel. It's difficult to fit low-riders on most MTBs in which case you'll have to fit a pair of panniers on a rear rack and just try not to take too much stuff.