Bring me... a shrubbery! Or a perfect donut (yah, they contracted it out
).
Traditionally, fae have trouble creating 'real' things. Make something. A perfect homecooked meal. Or, a perfectly RUINED homecooked meal.
A typical Mab-type request would be "do this seemingly simple thing that, while you're doing it, will coincedentally violate or negate the letter of a promise I made." For example, sending Harry to do just about anything in a building, that just happens to contain something you want burned.
Assassinate another fae. In some stories, a faerie battle had no real deaths, and so no winners or losers, unless a mortal participated.
Eat me.
Just about anything that will offend someone other than the police. Capturing dewdrop fairies? Not illegal. Taking a tree out of a park? Not illegal for this park, but will make the creatures that do rituals at the tree grumpy.
Oh, this is a fun one that might or might not be illegal, depending on your point of view. The famous painting in the art museum is a fake. Here's the original. Switch the two. Sure its breaking and entering, but you are also undoing a forgery.
Find the counterfeit dollar bills. Normal money is worthless to a fae, but a worthless thing that is treated as valueable but is therefore worthless to a fae, is oddly interesting.
Get me a backstage pass to the Elton John concert so I can capture his music.