If you are finding that you have to supplement your PPI with something like Gaviscon on a regular basis then you should ask to either increase the dosage or try a different PPI. In the meantime (or if you are worried about PPI side effects etc) try Asda own brand gaviscon, big bottle for under a fiver and much thicker (and I find more effective) than Gaviscon.
I have had gaviscon prescribed before when I had to go off rabeprazole in preparation for an endoscopy but that was a while ago, no harm in asking though.
Seeing as you have asked about diet/general advice to help with symptoms:
If you smoke, give up smoking (it makes your stomach empty at a slower rate)
If you are overweight (which puts pressure on your internal organs) try to lose some weight
Sleeping with your head more elevated, or lying on your left hand side can help reduce night time reflux for some.
Avoid tight clothing e.g. restrictive waistbands
Avoid (if you can) repetitive motioned such as repeated bending over at the waist
Common triggers include spicy food, chocolate, acidic food (fruit juices, wine etc) white bread but vary widely between people. Some people are soothed by drinking milk whereas others are set off by dairy. Keep a food diary to see if you have anything that makes it worse for you (or makes it better).
Be wary of old wives tales, drinking vinegar to balance pH is nonsense ( basically drinking acid to make your stomach less acidic), drinking vv hot water is probably not good either. I've also seen people recommend taking handfuls of ibruprofen with coffee, both of which will just irritate your stomach lining. However if desperate a teaspoonful of bicarb in a glass of water will help neutralise acid (but only very slightly) as will a sachet of those cranberry drinks you get for cystitis (again asda own brand are good, £1 for 6 sachets).
If you take regular medication make sure to take it before symptoms set in (ideally before breafast to give it time to start working properly), or preemptively if going out for a meal that might set things off.
I hope you find something that helps.