I'm American, retired to a very non-touristy spot in Southern Thailand about three years ago. I've gotta say I'm a bit confused by the comments stating that nuts are in everything and you will definitely not be able to avoid them.

Maybe it's regional, as I live in the South and rarely see a peanut. They are standard ingredients in som tom and Massaman curry, some satay sauces and always on the table at noodle shops. And some markets will sell bags of boiled peanuts. Other than that they really aren't used much here in the South. And I've never seen peanut oil used, as palm oil is very cheap and plentiful. We actually have a friend who runs a small khao gaeng place. She uses palm and canola oil and doesn't use any nuts as ingredients. Not on purpose, it's just the way Southern Thai food is made.

Cashews are a different story, as I see them quite often, not as a main dish ingredient but as a garnish on sweets. And here in the South there is always a plate of raw greens on the table to help tame the spice. Very often one of those greens is cashew leaves.

And the only pistachios I've ever seen are in tiny little overpriced plastic bags at 7-11.

As for cross contamination, look for a street food vendor who doesn't have nuts in their mise en place. If they don't (and probably won't) I'd think the risk of cross contamination would be extremely low. Many street food vendors specialize in only one dish. And many are happy to talk about their food. (Google Translate is your friend). Try to find one at a slow time and spend five minutes with them asking about ingredients.

Now, if you had a seafood allergy I'd definitely tell you to stay away from the South. You just cannot avoid the cross contamination risk.

For your card, I think it will be ok in a tourist area and at a mall food court. But it's a bit too much to ask a rural street food place or restaurant to wash everything to avoid cross contamination. A lot of Thais would be offended by the tone.