When I receive free snailmail return address labels by local, state and national bonafide and serious public policy campaigns for donations to worthy causes such as ALL various charities begging for a donation, I keep the return address labels and use them over time. Also, I throw away the HELP US DONATION reply envelopes but scan the barcode for free future postage stamps.
Thrifty and wise in these days of huge deficicit spending, I say!