The 'just add water' items or maybe an egg or just a few simple pieces. Not really looking for main dishes, just some fun extras to try in my new oven. If you're mentioning brownies or muffins or breads or cake mixes, maybe some brand names that worked better/went together simpler for you. Even owning up to any complete failures you've experienced would help. Thanks.

Well for Biscuits I use the Betty Crocker Bisquick Completes. They have 3 Cheese, Buttermilk, Garlic and plain. Easy to use, just add water and bake. I mix them in a large freezer bag with the water and then cut off a corner of the bag and squeeze it onto the tray to bake.
For brownies I have used a mix that comes in a red plastic shaker bottle. I leave that at home though and put it in a freezer bag and it's a just add water mix.

For Pizza, I use either a already prepared crust or a pizza crust mix.
Otherwise the Jiffy mixes are good to use. I've used the Cornbread one a lot. If you are taking cold food then you could use the refrigerated rolls like Crescent rolls, cinnamon rolls, etc. I've done those when car camping or on overnighters.

I use a jello mold oven rather than reflector but I've had good success with all of these mixes and bring them regularly. If a mix needs milk instead of water I just add an appropriate amount of powdered milk.

Thanks to both of you. We always have vegetable oil and spray butter substitute along, but to grease the pans, I'm thinking of a small Tupperware container of Crisco. I would guess that an aerosol can of Pam must be a no-no.

Cresco works great. I use it a lot when using JMO. As for PAM being in a can and a no no, I think you could get by with it.

I bring some of this in a small GoToob. Squeeze into jello mold and spread over interior with a small piece of paper towel

I use squeeze parkay for all oil needs but planning to switch to ghee. (I take oil also if someone is planning to fish - rare on my trips.)

Try scalloped potatoes and spam. Just open a box of scalloped potatoes and cut up some spam singles.

Been wanting to try that in a JMO - Spam and scalloped potatoes.