I have Celiac, its takes a while but eventually you learn what does and doesn’t have gluten.
Always read the labels, and learn the keywords that can mask “hidden” gluten. For example if it just says vinegar on a label, don’t buy it. Chances are its distilled white vinegar, but there is always that chance its malt vinegar.
Avoid all grains on keto anyway which will keep a lot of things safer. Soy sauce can be gluten free, but you have to be careful again to read the label as most soy sauce in the US is made with wheat.
If you are currently eating a lot of salt, you can also try restricting your salt for a while to see if that has an effect on your water retention.
Its best to stick with food that look like what they are. Meats and vegetables that haven’t been processed.