I've kept a few of the high denomination kind ($2 and more) from friends and family to whom I have sent packages. I've just asked them to cut off the whole square around them and include in the next letter of package heading my way.
Tally up the face value, photograph the group in organized piles and sell them on eBay. A lot of dealers (myself included) ship items for free. We use older stamps for postage that we have purchased at reduced prices. Many, many unused US stamps have face value only. They just are not worth anything.
One of the saddest sights around is to attend a large stamp show. There are so few young people interested in stamps. But in other countries stamp collecting is still doing “ okay “ and sales can be good.