While the Delta $50 GC trick was working, I would screen cap the GC number and PIN, then save that in a sub-folder within the CC folder. I have a folder for each card, such as Platinum, Aspire, and Gold, with folders for each year, to save the monthly statement PDFs. So an additional folder for "Gift Cards UnUsed".
Then, as a GC got cashed out, I'd move that image file to another folder, "Gift Cards Redeemed". I have one remaining $50 Delta GC in one of these unredeemed folders.
The other travel credits and free nights are kind of mentioned in my spreadsheet to keep track of various points, but that mostly is used to refer to the card / program website where the next steps need to occur.
High Bal Jan 2009 $116k on $146k limits 80% Util. Oct 2014 $46k on $127k 36% util EQ 722 TU 727 EX 727 April 2018 $18k on $344k 5% util EQ 806 TU 810 EX 812 Jan 2019 $7.6k on $360k EQ 832 TU 839 EX 831