Well, there are lots of ways to look at this, and your level of fitness is the biggest factor that we can't really judge here. If you're in great shape and really strong, you might have a pleasant time carrying a third of your body weight if the pack really fits well. But you'll have more fun with a lighter pack. I find staying under 20% of my body weight makes for easy walking and a pleasant trip. More than that and it starts to seem like work.