Over Christmas/New Year, I recently did a 9 day ride (Brownsville to Austin). Here is how I planned it out...

1. Before I left, I did some looking on Google Maps and on internet to understand:
- what towns had motels
- how far apart these towns were
- create an approximate plan, along with multiple alternatives
2. Before each day ride, in consultation with paper and internet maps, I had an approximate route figured out as well as a few choices:
- perhaps at most half a dozen turns in an entire day. Nothing too complex, but more like
"US281 through Pharr; once I reach Hildago go right towards US83"
- first motels will be in McAllen (~55 miles) and then mission (~70 miles). If things go well, there is also one in La Joya (~80 miles).
Some places things the choices were more constrained, but if I could I had a few alternatives to pick from and decided as I went along.
3. During that week, there was a major front that blew in - so during some of the evenings I made some bigger choices. For example,
from Laredo, I could have gone to Carrizo Springs - but decided to go to Freer, TX instead. I also decided to spend a day or two in
San Antonio rather than bicycle in the most extreme cold.

Those had been possibilities when I did my first assessment [step #1 ], but I waited until I was on the road to make the choices.

If I'm on a trip longer than just a week, I also try to keep that level of flexibility. Keeping an eye on an overall mileage "budget" and an overall direction I am headed. However, I'm not going to get things down to level of detail that I even have pinned down a precise "predetermined route", so I guess I deviate all the time...