Vintage Envelopes

The last trip we made to Austin we found a parking lot flea market.  All manner of things were being sold, but I ran across a vendor that had bins full of old envelopes.  I found myself digging through them for quite some time.  I don't know what it is about paper goods that have a little patina, but I'm smitten. 

I purhcased a few of my favorites.  I couldn't beat the 4 for a $1 special.  I'm not sure how I'll put them to use but I'll make room for them until an idea comes along. 

I picked this one up because of the train and the rural America stamp.  For whatever reason, the railroad was significant in my childhood.  The tracks split our town and until the viaduct was built to drive over them you had to wait until the train passed.  Many memories seem to have the tracks running through them.  I pitched hay next to the tracks, you didn't want to live on the wrong side of the tracks, as a teen you belted your music with the windows down while waiting to cross the tracks...  A grade school field trip was a ride on a passenger train from one town to another.  Then recently, my mom sent me a text about a steam engine train making a hisitoric run through the state.  Trains and tracks remind me of home, so this one made it on the purchasing list.

Any ideas on what I should do with these?