A Micro cache is the smallest of geocaches. Its size varies from a 35mm film canister down to smaller than your little finger. Typical containers include small pill containers and 'Yowie'/'Kinder Surprise' containers. Because they are so small, swaps are usually not part of these caches.
In many cases there most likely won't be a writing implement so take along a very fine pen. The log will also be very small and so most people usually write only their team name and a date. Any other notes are saved for when the find is logged on the cache page.
They will generally not have any swaps included.