The mimic finds the spinach salad to be bland and disappointing, almost exactly like the person who gave it to him! He spits out a mirror in order to share this sentiment.

I feed the mimic a box of Crest Whitestrips™

(I don't mean to insult you @GenderNihilistAnarchoCommunist, this is just how the mimic feels)

A buzzing sound is made as the mimic shreds the broken chair like a wood chipper! However if you look closely each of the shredded bits of chair are actually perfectly carved miniature chairs! 1000s of them! If only we had an army of tiny people to sit in these chairs!

I feed the mimic The Necronomicon

The mimic shiftily looks around and pockets the book quickly. In return he gives you Ring of Psychic Resistance.

I feed the mimic a tray of gas station sushi.

The mimic gulps down the antacid and slowly begins spewing out a large swarm of ants that just so happen to spit acid!

I feed the Mimic Boba Fett!

Boba Fett communicates with the Mimic's mind from within and eventually escapes, just like with the Sarlacc Pit. 

I feed the Mimic a Sarlacc Pit. 

The mimic spits out a sarlacc.

I feed it horse urine.

It spits out... More horse urine! You're soaked!

I feed it a slightly smaller mimic.

You are teleported to the astral plane, and the mimic stays where it is.

I proceed to feed it my +3 greataxe of tarresque smiting.

The mimic swallows the greataxe with gusto. It spits out the molten steel from the axe head, drawing a lopsided smiley face.

I feed the mimic a handful of red flintstones vitamin gummies

The mimic noms the red Flintstones vitamin gummies and quickly does 1 million pushups in the span of 3 seconds. He is now super charged and begins running circles around everyone in the room at high speeds and spewing candy and treasure!

I throw 1 banana peel at the mimic's feet :P

The mimic glances from you to the banana peel then back to you as it slowly uses its tongue to lick up the banana peel. It tosses it about in its mouth for a bit and spits back out to you a tongue tied origami swan.

I feed the mimic a mimic miniature.

The mimic chomps down on a few bits and pieces, a quizzical look on its face. After a few moments it spits out a Nokia at your feet.

I feed the mimic super glue.

The mimic gulps down your super glue and spits out a pile of things that were once broken but now fixed thanks to your contribution of tasty super glue!

I feed the mimic one extra extra large super deluxe pizza with every topping known to man...including a man...well the pizza delivery guy kinda got stuck to it. All that extra cheese can be sticky.

The mimics mouth dries with your terrible gluten-free concoction of fruits and straw.

I feed the mimic water.