A paltry amount is so small it's not even worth thinking about. In the novel Oliver Twist, when Oliver is given a paltry amount of gruel — not nearly enough — he asks, "Please, sir, can I have some more?"
Paltry is a laughably small amount — the waiter might chuck a paltry tip in the garbage. If you have only 50 cents in your bank account, it's such a paltry amount, you may as well be broke. It can also mean "not worth considering" or "not important." If you keep breaking your promises, your friends will get sick of your paltry excuses.