Don't say meat.
I am a meat eater but bought a bag of mixed/chopped veg which I now have in the slow cooker with a veggie stock.
Its new to me so wondering what I can add.
In the first instance, lentils (wash them first) for protein and thickening, a tin of tomatoes (if you like tomatoes) and some onions you've browned off in a little oil (if you can digest onions).
Then, if this is going to be a meal, think of some starch. Are going to eat it with hot bread rolls, or do you want the soup to be a meal in itself?
If you want it to be a meal in itself, at some point it will need some starch adding. This can be a grain (rice or pearl barley are probably most common) or potatoes - probably cut into small chunks. You can also use pasta of various sorts - there are some types expressly made to go into soups.
Then you need to think of what herbs and/or spices you like. I'd add a very little salt, plenty of freshly-ground black pepper, and a lot of paprika.
Stick em all in together and leave to simmer in the slow cooker. At several points, taste to make sure everything's cooking and the flavours are developing as you like. Add whatever else you think it needs or could benefit from. When all is cooked, you can either serve as is or blast in, or with, a blender/processor to the thickness/texture you prefer, or pass through a Moui mill to make a puree. or do half-and-half.