Your fingerboard will have to be converted to the metric system for use in Europe. This is especially important for 12 string guitars.
Dueling has been outlawed for many years so banjos are limited to one only per group/combo - trombones have no such limit (76 has been noted at some performances)
If you intend to visit Ulster with a marching band you will have to do it in season. This does not apply to the rest of the UK or Europe.
The import of steel from the USA will not effect stringed instruments but triangles have to be declared by weight - dont forget to include the beater in this or you may suffer a penalty.
Coonskin hats and some other ethnic items of apparral (Snake belts, cowhide boots etc) made from animal pelts may also be subject to quarantine regulations, so send them ahead by not less than 3 weeks prior to your arrival.
There is a sliding scale on size of tip-jars to be used, depending on number of performers in a group/combo. If you do not have a sliding scale a capo may be substituted.
Shape notes must comply to EU regulations.
Hope this helps :-)