We bought $300 in $100 increments in November, AAirlines and it worked (multiple cards here). Oddly enough, you can use the GCs for flights, but not for the extra things that the credit is initially good for (like upgrading seats and stuff like that). I was able to purchase AA seats with the GCs, but then had to pay with a CC for the premium upcharge on the seats, which meant a phone call to AA since it wouldn't work online. So kind of a pain, and no you can't use it for just anything, but it worked out for me since I had more AA tickets to purchase anyway.
As for the Saks money, I used it to buy skincare products I use every day. It's stuff I was going to buy anyway, so that's one way to use it up.