Yep, Ive had my credit card put on hold unexpectedly a couple of times when all of a sudden I try to use it in another area of the country, or in a way I never have before.
I always carry ~$100-$200 cash
Many places wont take plastic in small towns, esp on AT.
If you do mail drops, put cash in each mail drop. Its controls spending tightly. Cant spend what you dont have.
I mostly use my card to get cash from ATMs.
There is no reason to have, or use, a debit card.
I pay for just about everything possible with credit cards that doesnt cost me more. (for instance, cant pay daughters college tuition with them without 4% adder) I may spend $20,000 per year, but get back several hundreds of dollars per year in cash/airline/hotel points as long as pay every month, and use no-annual fee.
Debit card doesnt offer this, so no reason to use it.