You always have something of value. *pokes and prods eeph's arm, like a melon* Don't mind me, I'm check your ripeness. <img src="/images/graemlins/grin.gif" alt="" />
Seriously, I would never pretend to have nothing. I'll pretend to have less than I have, absolutely, but I want to be able to keep things cordial. If you act like you have nothing, and you aren't naked, someone is going to introduce your head to a length of pipe and take your gear. Maybe robbed vs definantly robbed.
We had this thread in long term a few months ago. It includes a wonderful post on bartering ettiquette in area with DIY normality.
The question is, how long of a situation are looking at? At a few days, I'll trade the smokes that I keep as trade goods in my BOB. At a month, I'll trade from a stash of things like needles and fish hooks that are set aside for that purpose. At a year... I'm trading my brain. Call me Mr. Wizard: I can make black powder, including getting the nitrates from manure piles (yuck!), make a still, and tan hides, among other things.