| This note arose from the variety of fascinating responses to a hypothesis I posited in order to explain an earlier sociological observation of mine, namely that Cigarettes are quasi-community property. In reading the responses, I have detected the hint of a corollary to this hypothesis which is perhaps less interesting but no less applicable. Namely, personal items, in other words objects typically carried on one's person, can be 'graded' on the degree to which they can be considered individual property as well as the degree to which one can reasonably expect a polite person to lend the use of them when asked.
In specific, this is the corollary: The communal nature of these items (pens, lighters, cigarettes, toothpicks, handkerchiefs, pipe tools (the smoking kind of pipe), marijuana, tobacco, even extending down to candy, gum or mints) can be lowered by personal sacrifice- that is, to carry a more expensive and/or harder to obtain version of the item. This is, of course, especially true for consumable items such as tobacco and weed products, candy, and booze (hip flasks forever!); but it works in other ways as well. For example, "Can I borrow your pen?" can be answered in the following ways, in increasing order of Pen Expense:
You can likely guess the type of pen/situation for each. In the first case, it's likely a cheap-ass biro/bic. In the second case, it's either a slightly more expensive but still expendable variety (Uni-ball Micro, GelRoller, Parker disposable fountain) or the person in question might add "It's my last one!" (note similarity to cigarettes here). The third is typically indicative of a long-held pen of greater monetary and/or personal value - a Cross Executive ball pen, or a lesser pen (like the above) that has displayed the one-in-a-n characteristic that the owner likes, like writing smoothly on their favorite checkbook, or perhaps having a very tasty barrel, or even having been chewed to the right consistency of softened plastic. The final option is the Nuclear Weapon of pen snobbery and Moocher Defense: it indicates the speaker has decided to armor themselves against all the scurrilous pen thieves that pervade our lives by carrying an actual writing instrument - the high-quality fountain pen.
The above example can be extended into lighters, pocketknives, bottle-opener keychains, and the like quite easily.
The other category, consumables, is more difficult to standardize but much easier to describe. It can be summed up in the phrase "Dude, no way can you get my grade-A blunt; that's for me."
This can, of course, lead to interesting processes of deciding which grade of Scotch to put in one's hip flask before the game, from whence one can deduce (for example) the likelihood of the owner taking secret nips or offering it around. | 
