CurriedCarbs they go to the bar and by their own drinks or order from the table, waiting staff arrive back with order, take money, then bring back change (or have change on them). This may be an Irish thing as I can't recall if I've seen in England (where I'm assuming you are). This arrangement with lounge staff can be standard enough in Ireland, can happen in pubs on a bog standard night out too.
Wedding services (church, registry office or service at the location) are simple enough. No difficulty there with expectations (Well generally no difficulty!)
What follows seems to cause mass confusion and disbelief on MN. Lots of people never go been to weddings where all drinks aren't free on the same thread were posters have never been to a wedding were they got a free drink.
Anyway, when i am invited to a wedding which is taking place in a hotel i would expect to have to dress up and bring a gift. I'd als probably arrive with the expectation of:
Drink on arrival (free)
Several course meal with wine* (free)
A drink to toast** (free)
Drinks after (guests buy - possibly be wine still on table so wine drinkers finish those)
Evening/late night food (free)
*quantity varies: either what's on the table or they get replace.
** glass of something bubbly or ordered by waiting staff from bar.
However where I've been invited to a wedding at a resturant and I'm aware I won't need to dress up or bring a gift. I don't think I'd even have the expectation of getting the meal for free. However as these are usually small/intimate weddings I'd ask the bride or groom what sort of price the food was (for my own budgeting) and this leads to the information about food and drink provision!!
I'd say you'll be grand CurriedCarbs. The resturant you've booked will cope with guests paying for their own drinks. Chances are it won't be that boozy anyway,