Back Story Rewards

Short Back Story
+1 to one Stat
Extra Skill
Learn an extra weapon (Such as Wizard taking rapier or long bow)

Medium Back Story
Earn a feat at 1st level
Item of quality
Memorize an extra spell or cantrip
+1 to two stats

Long Back Story
Additional use of a class ability (Channel Divinity, etc.)
Minor magic item
Extra 1st level spell slot
Choose one Short and one Medium bonus