Waste not, want not. When in Rome, do as the Romans do. You can lead a horse to water, but you cannot make him drink. You can't make a silk purse out of a sow's ear. Let sleeping dogs lie.
Hunger is the best sauce.
A rolling stone gathers no moss. A bird in the hand is worth two in the bush. A friend in need is a friend indeed. You know, it's like when you have a problem and only your true friends come to help you. All the other 'friends' will suddenly have no more time for you.