That's true, but there is only so much a missionary can do without. And playing cards is usually one vice they all have. At least the missionaries around here anyway.
1. Almost anything can be construed as being contraband under the missionary rules.
2. Most missionaries are fairly lax about the rules, especially when it comes to personal possessions. Most missionaries in my mission had trunks full of stuff they technically weren't supposed to have - "unapproved" music, comic books, guitars, harmonicas, posters, "unapproved" clothing, pin-up calendars, art supplies, pocket knives, toys, pets . . .
I bought a poker set while serving my sentence. I taught quite a few guys how to play. When it was time to go home, i left the set with someone to continue passing the joy.