The weather is glorious is Scotland just now.. looks like we're on track for a great summer as well!
Not too much to add after previous posters, apart from being 99.9% sure that it'll be a cash bar!
They may have a ceilidh, which are great fun, but you'll want comfortable shoes (i've been to weddings where all the women basically took their shoes off after dinner, in preparation for the dancing, but that was an islander wedding)
The last 2 songs of the night tend to be The Bonnie Bonnie Banks of Loch Lomond and 500 Miles. All the guests get in a big circle round the bride and groom, join hands and run towards them and away for them (it sounds odd but its really fun!)