When private goods become common

It’s something that I noticed quite quickly after coming to Lesotho: Coca cola in a large bottle can never be a private good.

So often I have a 2 liter bottle in the office and so often anyone who passes feels they can ask for a cup of it*. What is interesting though, is that this does not happen to any other drink. For example, fanta or fruit juices do not attract the same attention. Why should that be?

There is another interesting pair of private-common goods: chocolate on my desk is private; it belongs to me and no one will ask for it. Biscuits, on the other hand, are a common good. Anyone is allowed to ask for a biscuit.

I guess every society has similar things. In Europe, cigarettes used to be common-ish, but are now private, but that reflects a price change. Coke and fanta cost about the same amount here.

What other interesting combinations of these have people spotted?

* Interestingly, conditions apply. There must be no one else in the room and, most importantly, the coke must be cold. Warm coke appears to have about the same value here as sunblock on a rainy day. The Basotho are a people of taste :)