I would say the most problematic would be the CPU cooler, GPU, and HDDs.
If your CPU cooler is big and heavy, you need to make sure you have some strong backplate that will not allow anything to bend or break.
The GPU - the same. If it`s big and heavy it might be affected, so here it would help if you have a backplate on it.
The HDDs might get damaged if the trip is bumpy.
All in all, if you are very carefull with it, and the unit will not receive any shocks, it should be ok.
Also, if possible, carry it on a side, the way that your mobo is placed, and not standing.