If you're going to send me a postcard I can write you some ideas:
★ art (!)
★ Jewish-themed cards (synagogues, cemeteries, people etc.)
★ religious-themed (churches, mosques, temples etc.)
★ view of your town, village, city
★ everything connected with history / historical postcards
★ retro / nostalgia / vintage
★ something specific to only your region and country
★ national clothes, buildings, traditions in general
★ UNESCO sites
★ beautiful nature (I love mountains :)
If possible, please, don't send handmade/self-made postcards.
Have a nice day!