Probably the most effective way of saving money when out and about, is to simply not have any on you. It is very easy to avoid temptation of swiping a card or handing some bills when doing so requires you to go all the way back home for you to do it! I mainly do this only when I am in deep financially.
Not only does those small bags of potato chips or that 1$ hamburger at the Mcdonald’s drive-thru add up over time, but you are also prevented from making impulse buys. I don’t make any when I am without my card, which saves me all that money. I am able to counterbalance hunger though, as I always have some kind of snack in my bag for whenever I am feeling those hunger pangs.
Another way to circumvent this is to keep a fair amount of money in an cardless account. I use Betterment to invest my money, and it works exactly like a savings account. In fact, better than a savings account, as it increases the amount of money you have over time! Betterment takes 5 days to withdraw funds, Since I cannot just transfer funds when I desire a burger, it helps me to simply take out money when I really need it!
Having my hours cut recently and calculating my expenses, although not entirely bad, showed me that I was going to have to restart my No Card policy. What works even better, if if you are going shopping, to bring just what you need, maybe a dollar or two more. This way you only get what you went out to get, and not everything else in the store. I have a set budget of groceries and essentials of 150 a month for 3 people, I am going to strive to stick to that.