If I don't have access to my normal medication (Omeprazole) for any reason, I take half a teaspoonful of bicarbonate of soda in a glass of water, and at night keep a glass with some stirred in within reach. It a heck of a lot better than nothing. I've tried Gaviscon but it made me nauseous.
Regarding the endoscopy, it is very, very uncomfortable if you just have the localised throat spray anaesthetic, I must have been in quite a state, as the nurse was stroking my head as if I was a favourite dog taking its last breaths. The upside of the spray anaesthetic is that you can leave the hospital the within half an hour of the inspection and are able to drive home.
A strange side effect of the inspection for me was caused by the air that is blown down a tube on camera probe. As an asthmatic, having air blown down my throat was equivalent to supercharging me, and must have put a lot more oxygen into my blood than I get from normal breathing. I felt really quite invigorated as I left the hospital.