This is what Cecil Williamson had to say about get lost boxes in general and one in particular in the Witchcraft museum collection:
“It was common practice to consult your local witch when you wanted to get rid of someone or something. Often the witch would place a representation of the problem to be banished in a 'get lost box' and leave it at a crossroads. Liza Pengelly of Saltash who made this one always put her boxes inside a stocking. 'Liza Pengelly of Saltash always used a sexy ladies' stocking for her take-aways - and still does.' Some Swiss visitors told us that a method of curing illness still used in Switzerland consists of the sick person putting a piece of rice paper in their mouth, visualising the illness passing from them into the paper, then putting the paper into a wooden box and putting the box on the fire.”
As I’m sure will be clear the details of any one given ‘get lost box’ will be dependant on what you wish to get rid of a person, skin condition, illness etc.
I will give a basic (non Sub Rosa) run through on making a get lost box for skin conditions as I was told. Though normally a box other containers would do.
With your knife lightly scrape over the skin were there is a problem manifests so as to scrap some thing of it onto a piece of paper, flakes for dry conditions discharge for wet. Fold the paper with the sample, being aware that the essence of the condition is held within. Place the paper inside a box and then bind with red cord or other material the fancier/attractive the better. Leave at a crossroads, when someone pickes up the box and opens it the condition is transferred. Which is why it is not uncommon for grand parents and even parents in some places to warn children not to pick up strange objects especially at crossroads.
Another closely related method this time for warts is recorded in "The witchcraft and folklore of Dartmoor" by Ruth St Leger-Gordon 1965 I think it would be worth quoting the relevant section:
“By some witches the patient is instructed to go home, count his warts and put the equivalent number of stones or pebbles into a bag which he must then throw away, preferably at a cross-roads. I know a woman now about fifty, who, when in her twenties, adopted this procedure.
At the time, she explained to me the danger of picking up ant package found lying by the wayside. If, however, curiosity over come caution, the packet should be kicked first to ascertain its contents, for should it contain "Wart stones", the finder would automatically transfer to himself someone else's discarded warts..."
The whole book is well worth reading if you can get a copy.