My childhood favorite wet mount is the onion “skin”. The late Walter Dioni had many nice articles on it and how to prepare a good sample.  For example, see

http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artnov03/wdonion.html

The preparation was done rather carelessly but I was too excited to try out my Foldscope. The epidermis preparation was stained with a drop of Carbol rose bengal  (I bought this from the internet) for about 30-45 seconds and then washed with 70% ethanol (CVS) and tap water. Carbol Rose Bengal stains the nucleus brightly and gives a dainty contrast. If you look carefully, you can also see nucleoli. Taking pictures with the Foldscope was a bit rough at first as I was worried I might damage the microscope with the slide, but it is quite hardy, and with a few trials, it got easier. One thing I did was to tape the coverslip onto the slide so that it doesnt slip around while loading.