I have a new food saver vacuum sealer. I want to seal up all the ingredients for a slow cooker meal. Should I add the vegetables separately from the meat and sauce, or all in together? I was concerned some vegetables should not be frozen (such as onions).
If you're doing a one step cook in the slow cooker, you can freeze everything together. If you want to brown any ingredients first you'll need to keep them separate. I do tend to, so I'd have a bag for any meat, a bag for veg that wants browning or softening (onions, carrots, pepperd etc.) and a bag or other container for the liquid part, with any veg that doesn't need an initial step (beans, sweetcorn, potatoes...)
Most slow cooked dishes freeze very well after cooking, so an alternative is to cook several portions at once, divide and freeze, microwaving when you want to eat them. These approaches aren't mutually exclusive of course.
This is going to depend on how you want to use the items. If you are planning on combining several ingredients to put in a crockpot, then package them together (and move it to the fridge to thaw out the day before). If you are going to use (example) chicken in several recipes, then perhaps it would work better to package portions of meat separately (so you can take out what you need as you need it).
I'm sure there are things that do not respond well to freezing, but I cannot think of any off the top of my head. Just look at the varieties of vegetables in your grocer's freezer section. Onions freeze fine, btw. And most things do not require parboiling or any other pre-cooking methods.
I typically spread things out on a cookie sheet (cut, diced, or whole) and move it to zippered freezer bags after an hour (or so) in the freezer to prevent clumping. Corn on the cob doesn't even require that much work. Just pop them in the bags and stack them in the freezer. You can husk them and break them in half first, or if you prefer... put them in a freezer bag husks and all. Your choice.
Enjoy your new kitchen toy. I hope it saves you tons of time!
i have been regularly stewing and freezing for convenient meals for a few years. judging from the way you ask your question, I will guess that you are referring to freezing after the stew is cooked. your question is whether to separate the veg from the meat and sauce before freezing.
short answer is: there is no need to as there are no difference in the results you get. I tried both ways to reach this conclusion. like you I had concerns about what can freeze well.
tip: I figured out that I want to leave out root vegetables like stew favorites of potatoes and carrots, until the day you want to eat the stew. cooked potatoes and carrots do not freeze well, results in a lousy texture. So I only add in potatoes and carrots to cook on the day it is to be eaten.