I just saw these guys today with a table full of backpacks. They wanted you to buy a backpack and then immediately donate it back for kids in need to use as luggage during transitions. https://www.childhelp.org/states/colorado/
Actually luggage would be better IMO.
I contacted several groups who have 'outreach' programs in Colorado but are not based here... none of them were interested in gently used suitcases, only money.