If you take them in a small cage/plastic 'tank' type of thing they are mobile. They make some great 'transient' plastic cages nowadays. Just remember to put their needs first. If you're going to be taking them places, make sure that you have only two or three absolute maximum. Mice need space and get aggressive if they feel 'boxed in.'

Shelter them from noise until you get them to the destination, throw a sweater or whatever over the cage as they don't like a sudden change in lighting, noise etc. They are very small animals and to them the world is a huge and frightening place. Try to keep them stress free with minimal noise, bright light etc. If people approach them, (or yourself) always remember to place the tank/cage wherever you want it, and then leave it there if you can and come down to their level (i.e on your haunches) because if they see you looming over the cage they will get skittish as they think that you are a predator like an owl or eagle or whatever. Their eyes are oriented upwards for a reason, to look for overhead predators. Even 'domesticated' mice have this in built protection mechanism. Do as you would with a child that is shy, or doesn't know you very well. Come down to their level, keep your voice low, away from noise, and without harsh and intermittent light. Take some treats with you and try to get them used to associating you with good things to eat.

Also, make sure that they have a working water bottle, clean stuff for bedding, and food. They will need something to crawl into if they feel threatened, a small plastic or glass bottle laying on it's side and stuffed with toilet paper works well. Just somewhere to go and 'chill' if they feel stressed.

Just remember how small they are, and how acute their hearing and eyesight are, and put yourself in that position. To them, you're humungous. The world is noisy and scary. That's to be expected. Make the transition easy, and they're lovely to keep on your desk or wherever. Just make sure that they have enough space and something to entertain themselves like a couple of toilet roll inners to crawl through, a wheel, etc. Try not to hand them around like party favours, because you want them to get to know your smell and become familiar with you. Also, some people can be overly rough or get scared suddenly and drop or throw the mouse. This is obviously not good.

They are very entertaining and will give you hours of joy as you come to know their individual personalities. Just put their needs first and you'll do great. : )