That is the easy part.
The hard part is to make sure I understand the laws of each individual state, and make sure I am aware of any changes to those laws so that I can still maintain legal status while carrying when I travel.
The primary book that I like is "Self Defense Laws of All 50 States" (2nd Edition) by Attorney Mitch Vilos and Evan Vilos, and I use a couple apps on my iPhone including: Gun Conceal, and CCW.
I try to cross check these sources to make sure they all agree. One benefit to the phone apps is they have links directly to the state statutes in case there is a discrepancy. I feel pretty comfortable with this method but am always open to new ideas.
What do you guys do to ensure you are following the law while traveling with your guns?