As Trihan stated above, the tilesets B, C, D, and E, you can use as events when selecting an image. They're at the bottom of the list for MV. You can select any 48x48 (1 tile) asset to act as an event. However, the A Tilesets cannot be selected as events through the image selector (so things like walls, floors, etc), so if you wanted one of those, you'd have to copy them out of the file.
As for items, that's a bit more tricky. Items use the icon set (found in /system in MV, probably similar for MZ) to draw images from. You'll have to put the tiles you want into the icon set via an image editing program that allows transparency. This can be a problem, however, because the tiles are at 48x48 pixels, while each icon is 32x32. It's very likely the tile will not fit, but if it's small enough, you might be able to squeeze it in there.
Sorry if any information is not applicable. I'm using MV, not MZ, but I'm quite sure they'll be pretty similar in functionality.
No database entry ever existed on a map. No item, no equipment - actually not even actors or enemies.
The only thing you have on the map are events.
Events pretending to be NPCs, events pretending to be enemies, even a special character/event pretending to be the player/party but not really containing any of that party data.
You can make events pretending to be items, have those events vanish and add something to your inventory (that is basically what a chest does).
But the items themselves will never be on the map, only events pretending to be something else as long as you put the event commands in that helps the event to simulate the behaviour of that something else.
actually, are there any JRPG type games (I guess turn based, so not ARPGs like say, Vagrant Story) where you have only one party member for the majority of the game? (I wonder if I'm forgetting something obvious.)