In general is it a good idea to stock up on supplies?
 

Things like engine oil and oil filters for example.

Since they can last a long time, is it better to just stock up on them now since in the future the prices may increase??? Kind of like buying a good stock of 1st class forever postage stamps since they will just increase in price in the future.

I have 10 oil filters and 24 quarts of oil on hand. If you know youre going to keep the car, theres no sense not to save money when you can.

In particular, I'm eyeing Wal-Mart's low price for 5 qts of 0W-20 oil. Who knows if that price will hold steady in the future.

Only if opportunity arises, i.e. there was a 10 pack of filters that worked out to like $7/filter.

Don't bother seeking them out, there will be ample spare parts for years to come. This car shares a fair number of consumable components with other cars and OEMs know that they need to stock replacements for a couple years after they stop making the car. For instance, I bought a shift boot for my truck last summer, it was 22 years old at the time and they stopped selling it in America in 1997, I got an OEM boot from a Nissan dealer for <$15.

Edit this goes for oil too, 0W-20 will only become more common as manufacturers try to stretch out better efficiency. The combustion engine isn't going anywhere soon and with the advent of viable electric cars I don't think we'll be seeing the absurd oil prices we were predicting 5 or 10 years ago.

If you're looking for inexpensive synthetic oil, NAPA (see Valvoline) has their syn oil on sale this month for $3.49/qt. Filters on sale, too.

Most motor oil producers claim a shelf life of 4 to 5 years for an unopened container. Once it's opened, shelf life is drastically reduced. That being said, I've owned a lot of older motorcycles and cars; up until 2008 the newest, most modern car I'd owned was a '68 Mustang. My experience has been that the good vehicles are well-supported in terms of parts availability, while the really piss-poor ones can be almost impossible to find parts for.

Depends on if you have space to store it or not.
You may find yourself tripping over it in a small apartment.
Most businesses are going JIT (Just In Time) to avoid having to stock inventory.

I know at the dealership I work at we have a 3 filters for 15 deal that is always running. Of course washers are extra