You need to read about variable scope, how functions work and essentially when to use them. In my opinion, this is not one of those occasions.
See Number 6 Here
Or don't use functions. Your code should work perfectly as a subroutine - without the globals. Plus, you also have the ability to write data as strings.
me# = 0.0: Rem <<< Mote that 'me' is variable, NOT 'float'
you = 0
Gosub SaveGame
Wait Key
End
SaveGame:
Open To Write 1,"save.txt"
Write Float 1,me#
Write Long 1,you
Close File 1
Return
You also appear to be misreading the help files (or making things up as you go along) which unfortunately doesn't work.:
write float 1,"me"
You should read a few tutorials so you know what you are doing...
See Number 4 Here
Quite a few of the tutorials in that thread will teach you a considerable amount.
TDK