Question 1,
The best way to spend cryptos is to have your cryptos converted directly into fiat and after filling up at the gas station you have more coal in your account than before.

Regarding question 2. The best way is adaptation and dissemination. Atari started something that I see very far ahead, playing and trading a coin to swap.
Regarding question 3. We will say goodbye to the Fiat, to what extent will we see how many euros will still be reprinted. 5 years won't change much, the Bitcoin is 11-12 years old and can still be easily put into your pocket by one of the big Apple, Microsoft, etc.