Best way to select a number of items from a list, and then rearrange those items into an order

So I'm trying to create a menu that prompts the user to prepare a message that would soon be sent. I'm also using mostly WPF and C# if that helps.

This message will possibly contain a number of items, say, items A, F, T, X out of items A,..., and Z. But the user may also want to rearrange A, F, T and X into possibly F, X, T, and then A, so the message containing those items will send those items in that order.

How could I let the user pick which items they may want in the message and then rearrange those items into any order?

Thanks!