I'm not the most in shape of all people so might not match most people here. I did 30 miles yesterday to come visit my girlfriend, as yet I haven't got a rack for my bike so used my backpack, being slightly cunning I sent clothes ahead of me when my lady drove back from my house to hers. All I had in my pack was a litre of water, toothbrush, roll on deodorant, book, 10" netbook and relevant cables.
By the time I got to her house, I was drenched through with sweat and ached slightly, I'm really not looking forwards to the ride back tomorrow, and may skip the water and hope I can fill the litre bottle on my bike back up about half way or more often, instead of carrying it. (Memo to self get a new cage when I can afford it.)