Spare Car Parts
I keep a spare oil filter and 5 quarts of oil for each of my cars. Having these on hand does several things:
1 - Don't have to find out that it's out of stock at the store
2 - Ready right now, so no excuses for not changing the oil
3 - It was probably cheaper when I bought it, so saved some $$
It's a good idea to write on the oil filter box which car it's for so you don't grab the wrong one.
If you're so inclined, keeping spare air filters, plugs and other parts on hand will do you well should there be a SHTF situation and going to the store is no longer an option.