Minimalist Outing

A friend and I were having a discussion the other day about doing a couple day outing with only three supplies allowed.  Water and a backpack not counting as one of the three what would you take?  A pocket knife, a tent, sleeping bag, food, matches or maybe a weapon of some sort?  Keep in mind we were talking about covering 15 to 20 miles, so whatever you take it must be light and easily carried.  I think I would opt for a jacket of some sort cause it is still getting fairly cold at night, maybe a multi-tool, and then some sort of food like an MRE.  What are the three things you would take along?