Stick this button on a toolbar (see here if you've never pasted a button from the forums to your toolbars before):
<?xml version="1.0"?>
<button display="both" label_pos="right">
<label>Drive Buttons (Non-Empty)</label>
<icon1>116</icon1>
<function type="normal">
<instruction>Go DRIVEBUTTONS=labels,lettersbeforelabels,hideempty</instruction>
</function>
</button>
It will show all of your drives, excluding all of the empty ones.
(If you have a floppy drive it'll always be displayed since there's no good way to detect whether or not it is empty in Windows without generating annoying clicks every time it is checked. Everything else, like your empty memory card drive letters, will be hidden from the toolbar/menu.)