Obviously we can't have wands. As Muggles, we can't use them. It'll just give a “kick like a mule”  and send us flying if we ever tried. This also precludes artifacts such as the Pensieve, which require a wand to operate.
In which case I want a masterpiece of wizard ingenuity which is also Muggle operable:
Newt Scamander’s Trunk
Some of its features:
Literally acres of space inside with its own weather system. You won't be feeling the January blues if you can get your dose of Vitamin D straight from Arizona.
Food, water and fascinating animals (if Newt left them for me)
Shed and sheltered areas for living
Undetectable Extension Charm that gives it its huge volume but reduces the weight to that of a normal briefcase
Switch to fool curious Muggles
Imagine travelling the world, or living in the most interesting locales, without having to worry about rent, or housemates, or bills. Or if you just want a little corner to study or read in peace. On the beach. With sun.