You can use the SAVE command in conjunction with an array.
First, you'd define the array, which must be numerical and will hold the data you want to save. Afterwards, you can use the save command by specifying the file type as DAT and specifying the array. E.g.:
DIM SAVARR[3]
SAVARR[0]=HP
SAVARR[1]=XP
SAVARR[2]=IDK
SAVE "DAT:FILENAME",SAVARR
Similarly, to load the data back, you'd use another numerical array and the LOAD command. You can keep the array empty as it will be expanded automatically. All data will be in the same order as you saved it. I suggest wrapping the load in a CHKFILE conditional.
IF CHKFILE("DAT:FILENAME") THEN
DIM LOADARR[0]
LOAD "DAT:FILENAME",LOADARR,FALSE
HP=LOADARR[0]
XP=LOADARR[1]
IDK=LOADARR[2]
ENDIF
