This sort of thing blows my mind. So you're out with people you consider friends but you can't say either:
'I'm a bit skint this month so I'm going to pay separately if that's ok?'
or
"I'm not drinking, so can we split the food & Drink and I'll pay for my food'
Either one of these options is absolutely fine, if you do it at the start, there's no issue at all. If you wait until the bill has come then the only rule will be that you get on a pay yours quickly and make sure you get the new total correct.
Usually though, I'm in favour of splitting the bill as I hate having to wait for the receipt and read through what we all had and add it up and often the last person to pay has to cover whatever small bits the earlier ones have missed.
It much less awkward to just split the bill in my experience, usually over time, it balances itself out as there are sometimes you go out and it is in your favour, and other times not. So unless I'm proper skint, and the difference is less than say £10, I'll suck it up.
I only have sensible friends who realise this though, so it's never really been an issue.