The charitable organizations use the money to buy at wholesale. Cases of things are easier to ship, than individual items that need to be boxed, then shipped. We had lots of STUFF - clothes donated here that eventually wound up in the trash. It was amazing the odd stuff that months later we were sorting through trying to figure out what to do with. Yes we appreciated the thought that the nation was sending aid, and didn't want to seem ungrateful, but your miscellaneous garage sale items weren't really needed.

Unless at a local level, you can pack and ship clearly labled new boxes of supplies, such as the specialized items Ehirsch mentioned - just send cash. Impersonnal, I know, but effecient. If you are sending supplies, please check the expiration dates.