this is perhaps against the grain of most here but i almost always use the bag juice in its entirety, especially if i don't have some kind of other sauce in mind. some spices or salt and pepper, reduced/browned in the skillet in high heat, add fat or liquids as necessary and (as @btbyrd intimates) in the vitamix or stick blender to re-emulsify. generally works well, especially if you end up doing a sweet sauce (heavy spoon of tomato paste, some vinegar, mustard, and some kind of sweetener and you've got a quick and meaty bbq sauce, for example). i don't bother straining, that's too much work.
meat can be kept warm as suggested in an open bag in the water bath, or a warmed-and-turned-off oven, covered to keep moisture in. the sauce only takes five minutes to bring together so it's hardly going to be there for long.
