When I had 'quiet' days .... no taxis... just walking and a bit of time down beach I was spending a tenner a day.
Breakfast - Omlette + Fruit + Tea
Lunch - A Snack + Beer
Evening Meal - Curry Rice & Roti + Raita, either 2 Beers or 2 G&T,
This was weeks 3 and 4 of a month holiday where you tend to spend most money within first week and done a lot of trecking and taxi expenditure.
I have had days when I wasn't drinking alcohol and spent a fiver.
You can spend whatever you want really, it's really surprising how little you can spend if you are on a low budget.