some good ideas on here! i did this for marley yesterday:
brodo vegetale (its basically like a veg soup base which you can add baby pasta or cooked lentils to!, they eat it all the time in italy its yummy)
in a pan add:
1 big potato cut in half
i stick of celery cut in half
2 carrots cut in half
a few cherry tomatoes (whole)
1 onion cut into quarters
any other veg that you have really! a cabbage leaf, slice of pepper etc etc
bring this to the boil, when boiling reduce the heat and simmer for about 20mins till the veg is soft.
the stock can be used as a base for anything and will keep in the fridge for a good few days. i usually take out a piece of carrot and potato, mash with some of the juice and then sperately i cook some baby pasta shapes in the stock as well (so it becomes nice and flavoursome) and add that to the mash or puree. i also cooked some red lentils, and added then to some mashed potato and carrot from this stock. i also added a drop of extra virgin olive oil and grated some parmesan cheese in too. its really healthy and yummy... and CHEAP!!! =)) BUON APPETITO!!! =)