Leveling up mainly. Something about being able to see my own stats would actually drive me to exercise. Or every time i practice guitar, I get more experience and can unlock advance skills like shredding.
Saving game. You know you wish you could save before something big, and if the results are unsatisfactory, load game and try something different.
Random battles. Would make the day-to-day more interesting, and with an earnings system, i would never have to work a day of my life. Need money? Just go kill a few beasties and get rich. This also works hand-in-hand with the level up system.
Weapons and Armor. It would give clothes shopping a whole new value and for once i'd care about my appearance.
BGM [Background Music]. To be able to listen to my music library anywhere, anytime, without the need of headphones or speakers? Come on, that's a no brainer.