It's a long time ago, but my (now) DH and I always paid equally, usually one or other of us would pay and the other would hand over half in cash. I always insisted I wanted to pay my way. It was different on birthdays and other special occasions where one of us would "treat" the other, but generally speaking, we kept to everything being 50:50.
When on holiday etc., we even had an extra "joint" purse where we both put the same amount of cash in and used it to pay for "joint" things like meals, drinks, attraction entry fees, etc. We'd then use our own purse/wallet for things that only one of us wanted to buy, i.e. an expensive souvenir etc.
As we were both roughly "on the same wavelength" we never had problems where one of us had a more expensive meal/drink or an extra course etc., so roughly speaking, our "joint" spendings were equal, so 50:50 worked - we both had the sense not to take the piss by spending a lot more than the other.
Same on evenings in the pub. We'd take it in turns to buy the drinks and usually managed to have an equal number, whether 2 or 4 - to keep things equal.
My prior boyfriend was an utter nightmare, would ask for a shot when it was my round but half a lager when it was his, and would usually let me buy the first round, then decide he'd had enough after 3 so it'd end up with me having bought 2 and him only 1. Needless to say, he didn't last long before I binned him!
Ultimately it's what works for you. Need to be open with communications etc., sort things out in advance to avoid awkward moments etc. If you can't discuss in advance openly, then it's not a healthy relationship.