Interesting set of responses.
Our approach on most occasions is to split the bill equally but if someone is not drinking we initiate the idea of an uneven split. Not to pennies but equitable round numbers. Food split is always even.
Going out to footie games around the country is an interesting one. Always a varying set of folks and numbers. But we have evolved a varying round system. You arrive and buy yourself a pint plus anyone who is empty. Different folks repeat that on arrival or when empty. Result is sometimes you buy more than you drink, sometime less - on average it works out.
In Vancouver, it has long been table service only and the bill often comes itemised by seating position. Equitable splitting is then easy.
There is a guy in the local crowd who we no longer see... in the curry house if it was going to be buy your own, he had one dish and rice. If it was split-the-bill he had a starter and mixed grill.
Going to the pub, let's say there were going to be six of us. If 3 arrived, he would buy the round. If all six arrived he would hang back and buy later as round size reduced. If it was a kitty, last man buying topped up by a pound or two, this guy was never last man buying. His behaviour was noticed, and remarked upon.