There are at least two options. First, it’s always wise to return a gift or benefit of this kind if you don’t want to use it. This is true for all sorts of tickets, benefits, and other awards and gifts. It’s also always permissible to use those things in furtherance of charitable purposes.
My favorite example is tickets to an NFL game that the foundation received. They then turned those tickets over to the Big Brother Big Sister program so that they could attend the game. If that discount card would be useful or valuable to a grantee who needs to buy supplies, for example, to care for the homeless or children, you could always convert something owned by the foundation to further a charitable purpose, just as long as you don’t use it to benefit family members and insiders.