How do you handle the following situation?

You are standing behind a person [note no description of said person] in line at the grocery store. "Person" is a dollar or so short of meeting the tab for their items. The items appear to be of subsistence nature (is that important? Yes, for the sake of this argument). You have a couple extra bucks or coins in your wallet.

Do you
(1) Avoid any involvement in the situation.
(2) Say, "Buddy, I got it." and fork over what s/he owes.
(3) Roll your eyes, consult your watch, and huff while the cashier backs out a couple items so that Person can afford the tab.
(4) Try to engage others in a political conversation about immigrants, socialism, deviants or wastrels of any ilk?

I bring up this situation in an attempt to humanize "excellence", "equality" and all that jazz.

In our day-to-day lives, we happen upon others who may have needs, temporary or otherwise. Sometimes we're in a position to help, because we have a few extra coins, and we know they are in need.

Can't we look at these bigger questions with a more local focus?

And by the way, I think this forum has handled this initial post beautifully, all in all.