Long journey for me means that is a minimum 3 hours drive so things I like to check (when I remember) are:
- Oil level make sure is where it should be and never add too much
- Break fluid level, without opening the lid look for the min/max lines should be somewhere in the middle
- Coolant level same as the break fluid look for the min/max lines
- Fill up the screen wash
- Check your tyre’s pressure
- Check your lights indicators, long and short beam, break ones and reg plate one(s)
If all is good then I would say you are ready to go, and don’t say this took you 3 hours to check.
If I missed something comment bellow.