I have a small Omnigrid combo mat that I use at my machine when I really need to press as I go. Does Omnigrid make a combo mat that would be large enough to cut comfortably on? The combo mat is nice because you have the two surfaces in one and it is rigid which is nice.
As long as your mat can travel totally flat it should be ok. I worry about my rulers and stuff like that. I have had a ruler break enroute to a class. Personally, if you don't think you'll be pressing anything (or they will have a surface at the retreat) I would just bring my mat providing there is room for flat travel. I have little marks on one of my mats for special measurements so I would be lost without it but a pressing surface is less important to me.
I'm sure that some of the seasoned retreaters will have some good suggestions for you as well.