I would say "During the picnic" or "For the picnic" instead of "In the picnic".

Changed.

Changed once again.
I don't want to change it to "bring the tent", as the Hebrew variant (which was my original) uses the expression "to take care of something", meaning, to make sure it's there.

This seems to be a joke... but I don't get it. Someone explain it to me, please? ^^

It's strange. At the time, I got the joke. Now I see that it's not as funny as I thought it was (actually, it's not funny at all, unless we change something in the wording).

So what's the joke? I see no sense in it whatsoever.

What's the humour in it? Why did they have two tents, but no food?

The joke is that one of them got mixed up and thought he had to bring a tent while he should have brought the food... So both of them brought tents and none of them brought food.

I agree it doesn't sound funny at all, seeing the current wording.

I think it would be better if at Tatoeba there was a policy not to include sentences, even if funny, which are originally so-called ethnic jokes. We have a policy that all languages at Tatoeba are equal, and I think we should also say that all peoples are equal. When someone asks me: "Did you hear about the the Newfoundlanders who...?" or "Let me tell you about the Pole and the Ukrainian...", I turn away and say: "I don't want to hear it." So-called jokes which are intended to disparage a particular ethnicity as being supposedly stupider than other people work against modern attempts to bring people together worldwide.

Maybe to bring people together worldwide, is not such a good and shared objective.