Different clique practises different systems...so far these are
the systems I have encountered before:
1) Each pays his/her own share (My preferred system)
2) Each takes turn to treat
3)The one who is richer tends to pay...but later forgets to
collect money from us or subsidizes
4) Each pays his/her own share excluding GST and service
charge...the one who is more generous forks out the extra.