"Resources" is a loose term when it comes to putting together a game for your players, but for the purposes of this site the four main resources are Time, Money, Weight, and Ideas.
Time is often the #1 resource that as a GM I wish I had more of. Ideas or products that can save time are often worth their weight in electrum pieces.
Money is an obvious choice for something to save and usually doesn't need an explanation, but saving money doesn't always equate to the cheapest option. The Frugal GM is all about value versus cost.
Unless you never GM away from the family dinner table, weight can quickly become a problem, especially if you are travelling to a convention.
Often the most valuable resource in preparing a game for your players is a good idea. Whether you need help with a problem or just want to learn a different way of doing things, you shouldn't have to reinvent the wheel. A smart GM learns from his own experience, but a wise GM learns from the experiences of others. A Frugal GM is both smart and wise.