If we don't waste what we have, we'll still have it in the future and will not lack (want) it.
waste not, want not
Wise use of one's resources will keep one from poverty. For example, I just hate to throw out good foodwaste not, want not. This proverbial saying was first recorded in 1772 but had an earlier, even more alliterative version, willful waste makes woeful want (1576).