I lifted my trunk today and this thing was sitting in the well.
I can't find where it originally came from and if it's important.
Can anyone recognize it?

 

That looks like the little popper that lifts the trunk up a bit when you unlock it. It cam from the hinge on the right side as you look into the trunk. Not sure if you can tell where it came from, but there should be an open spot from where it fell.

 

As Alfadude said, the official name is "trunk lid latch actuator". See the black bit on the right side trunk lid hinge here:


There are two, one per side. The part numbers are different on both sides so you'll have to check which one you're missing. Also, there's a whole bunch of codes for these but apparently all were superseded by the latest ones.

Examples here:
LH: C2S46396
RH: C2S46395

 

How does the bracket itself come out? It appears to be a plastic rivet similar to the one shown at http://www.jaguarpartscheap.com/OEMP.../C2S16596.html but I am not having any luck compressing it enough to remove both of them without destroying it...and I had hoped to reuse both of them.