How do I create a weighted collection and then pick a random element from it?

I have a loot box that I want to fill with a random item. But I want each item to have a different chance of being picked. For example:

• 5% chance of 10 gold


• 20% chance of sword


• 45% chance of shield


• 20% chance of armor


• 10% chance of potion

How can I make it so that I select exactly one of the items above, where those percentages are the respective chances of getting the loot?