Summon Lost Object, 1/per day. I need this.
continues fruitlessly searching for things
Telekinesis. I’d never get ripped off by a vending machine again, or lock myself out of my car.
Mage hand cantrip could be useful in many mundane circumstances.
The DM power of “No Saving Throw”.
Teleportation.
The ultimate fast and secure courier.
Or just spend evenings and weekends wherever the fuck you want.
I agree. I was always fascinated by the skill in the book and movie Jumper. Though the only downer is having to actually know the place you want to jump to.
Charm Person–at will.
“I’m Mr Popular !”
Not that useful actually, I just think it would be cool to be able to randomly summon horses everywhere.
Prestidigitation. Two hugely useful aspects of it:
“It can color, clean, or soil items in a 1-foot cube each round.” Wiggle your finger for an hour or so, and clean a room.
“It can chill, warm, or flavor 1 pound of nonliving material.” The perfect kitchen accessory!
Arcane gate. Generates a Portal-style, uh, portal for 10 minutes at a time.
Use to violate conservation of energy. Deploy portals at top and bottom of large vacuum chamber. Drop dense masses through chamber so that they pick up tremendous kinetic energy, then harvest that energy using an electromagnetic decelerator. Make billions by undercutting industry, and pollution-free to boot. In slightly different form, can be used as a space launch system.
Also helpful in converting vertical momentum into horizontal in case I fall out of an airplane or something.
Summon Ally, for when I need a friend. 
I’m not sure – either a healing spell or some kind of Fireball. A healing spell has many uses. The Fireball is for when I’m out bicycling and am passed too close by a pickup/SUV (it’s virtually always one of those two). I’m sure an SUV has more hit points than a Fireball can dish out, but it’ll make the driver think twice about how close he is when passing a cyclist. Coal-rollers, BTW, get an Empowered Fireball.
Yeah but, what if it pushes the dirty out of the edges of the cube. You’ll just chase it around forever.
Probably the most mundane useful spell would be mend.
Would a sophisticated bit of technology count as “magic”? The link says “This spell can physically repair a magic item or construct, but the spell can’t restore magic to such an object.” Applied to the real world, that sounds a lot like “You can physically reattach the two halves of your broken smartphone, but you can’t make it work as a computer again.”
I’d like a Bag of Holding, as it would clean up the house a bunch. I guess I’d have to invest in Sterilite to avoid poky parts, though.
I’d like to like Polymorph at will, or better, the higher-level variant Shapechange.
Telekinesis. So handy for moving furniture, boxes, heavy groceries etc.
Then I’d be highly disappointed. 
Infravision. No more flashlights required.