If you don't so it already, meal plan. Buy everything "big" in the week you have the moolah. Meat etc. make it so you only have to get staples like bread and milk on the small week. Factor your petrol out of the bigger week. Work out before you get paid whether you have anything that involves additional travel and put fuel in the car.

I rejigged our budget last night, and on our small week, once bills wtf are paid, we have less than $50. Yes we have wriggle room if I don't pay a bill in advance, but like you I prefer to get it all paid. I say and worked it out and if we so our "real" shop when we have money to do so, bread and milk and maybe drag salad is doable for that. Dh is struggling with it - he's used to having ready cash all the time - but I'm sick if playing catch up with bills and thins so I've factored in everything to be paid, and he will just need to get used to the budget lifestyle (he doesn't realise I've been inofficiallu doing this for months and we've survived!)