I bought a one park ticket ; so do I have to only eat at the places in that park or can I go eat at the other ones ?

You can leave the park and eat at downtown disney. As long as you have ypur ticket you may leave and enter anytime

You can leave the park, but remember you can bring snacks and food into the park, it's allot cheaper.

You canleave the park and be able to return. You can also bring small snacks as well as water bottles. You might consider doing that . There are water fountains but they are few and far between. Hope this helps.

I think you answered your own question

You can leave the park and enjoy restaurants and shopping in the Downtown Disney area and hotels. You will not be allowed into the other patk.

If the restaurants are in the other park, then no, you can only enter one park

If you only have one a ticket for one park, you can't go into the other park. You can, however eat at downtown Disney and reenter the park after.