Just a waistcoat?

[KiltedSergeant]

IMHO.......first, I would ask your friend whose wedding it is of their opinion. Ask them how formal it is, and if they think a vest without jacket is acceptable. In the states, many weddings are fairly informal, even in the evening. Sometimes friends want to be accommodating, however, and might lead you into a situation where everyone else is in formal attire, and you're left feeling out of place. Is it a daytime or evening affair? If daytime it is more likely to be less formal. If it's in the evening, and formal, then wearing only a waistcoat would be inappropriate.

Talk to your friend, get them to be honest with you as to the level of attire, then you can make a safe decision.

One option that some here might find offensive, but I've seen it done, is to wear a Saxon jacket with the kilt. Most people at the wedding, unless they're kilt knowledgeable wouldn't know the difference. Another option- if the wedding is formal- is to rent a PC. It's not too costly, and might solve your problem.

Good luck.