I used to wrap the receipt with the balance around the card and then shove it back in my wallet. It was a hot mess.
My new and impoved solution? The cute little Sharpie on the right.
I found it near the check out at Lowe’s for 97 cents. It hooks right on my keychain. Now when I get the balance on a gift card, I take out my Sharpie and write it on the front of the card.