Depends on the scenario but one of the following:

• Shoot it off if its cheap crap
• Store it if its not great but will do in a pinch, and I only have a small amount
• Give it to someone (if its not too expensive, like under €40 or so quid)
• Sell it if its expensive or in large quantities.

Got some Fiocchi HP 50 gr stuff once. Two boxes cost €60 with 50 rounds per box. Fired about 12 rounds and they were terrible. Didn't know what to do with them then a young lad on the range was there with his new rifle and a small mix of ammo (looked like he had been given a few rounds of each type by someone else) and I gave it to him with the warning they were rubbish, but he was more excited about just hitting the target so gladly shot them for the rest of the day.