You can make a backup save by clicking "Export" under Settings. Just paste it into any text editor and save it somewhere safe. Serenitrove already autosaves, so backups are mainly useful if you clear your browser cache or want to move your save to another device.
For the slot machine, it is just an optional way to get some extra resources. You can ignore it if you want, though you will need to spend a bit of quartz on it to unlock one of the turtles and get an achievement.
As for tipping, I have disabled payments on Serenitrove. If you would still like to support something, consider donating to any wildlife charity instead. That would make me really happy :)