My DH, who is allergic to the world, carries 3 at all times. I own a few (including that small Mickey Mouse version from the 60's that I got with my First Day of School book bag), but now the kids are no longer small, I only carry them at weddings and funerals. Mine are embroidered and need to be hand-laundered, but DH's go into the washing machine. He folds them nicely and stores them in his drawer under a paperweight, but does not iron them, because starch makes them less absorbent. The kids always buy him new ones at Christmas, so the ratty ones are frequently thrown out.
My mother had us carry them to Mass and to school as children, but I was raised to blow my nose only in the privacy of the bathroom, so that's still my habit -- I use toilet tissue for that purpose.