Wine vinegar isn't a great substitute for wine - it's much more sour and doesn't have the richness of flavour. However, if you don't have wine handy a very small amount of balsamic vinegar can be used to add depth of flavour. I sometimes use a bit of brandy instead of wine, as brandy keeps much better than a bottle of wine, so I always have it on hand.
If you use dehydrated mushrooms, the water you use to soak them in is great for gravies and sauces. When I use dried shitakes I rinse them well with water (to remove pesticides and dirt), soak in warm water until soft, and toss the excess liquid in a bag in the freezer for later. For vegetarians, you can use that and onions in place of meat stock. If you cook dried beans or chickpeas, you can save that liquid as well, as a soup broth or gravy base.
For the powdered mixes and vegetarianism, if I remember correctly the phrase "natural flavours" can include small amounts of meat products (natural meat flavour is still meat).
For other sauces and accompaniments for meats that aren't strictly gravy;
Slowly caramelize onions in half butter and half olive oil, with a sprig of rosemary. When they are almost done, add some sherry and reduce until the liquid is gone. This makes a wonderful side/topping for things like pork loin, and is very good with chicken and a bit of blue cheese crumbled on top.
You can also make use mustard as a flavouring for things like ham or pork loin or roast beef. Make a simple flour thickened sauce with broth, and flavour heavily with a good dijon mustard.