drsoosie,
To thicken sauce, you can add xanthan gum. Just a tiny bit is needed, about 1/8 tsp. Stir in very well. Cold butter stirred in thickens, so does grated cheese, if they'll work with the type of sauce.
For things like pudding, I add corn starch. At 3 carbs tsp divided between a number of servings, the carbs are negligible.