1) Audio equitment. Buy cheap and you'll be wondering whether to recycle it or throw it out in about a year.
2) Trash bags. Cheap ones break, IF you can manage to open them.
3) Soda. Off brands suck
4) N2O. Guy selling two for five probably has industrial grade or helium.
5) Pillows. Why save two bucks if it will be flat as Herman Munsters head in a month.
6) Motor Oil. You're going to put an off-brand in your engine to save 90 cents?
7) Umbrellas. Cheap umbrellas must be designed for one use.

Cologne. Want to smell like Exit 16A?
9) Taxies. Its yellow or bust.
10) Cigars. If its not a least a buck, you'll just end up feeling sick.
11) Bus travel. If you can't afford Grayhound, don't go.
12) Water pistols. Do you want to shoot your friends or just end up with wet hands?
13) Canned pasta. You really think Chef-Boy-Ar-De it too extravagant?