Landships II

You might find out more from the Middlesex Regimental Museum - http://www.armymuseums.org.uk/museums/0000000069-Middlesex-Regiment-Collection.htm

A possible shortcut - the National Archives - http://www.nationalarchives.gov.uk/documentsonline/medals.asp - lists this medal card:

Medal card of Heiser, Gustav
Corps Regiment No Rank
Middlesex Regiment G/45999 Private
Date 1914-1920
Catalogue reference WO 372/9
Dept Records created or inherited by the War Office, Armed Forces, Judge Advocate General, and related bodies
Series War Office: Service Medal and Award Rolls Index, First World War
Piece Hampton E - Holland D
Image contains 1 medal card of many for this collection

Number of image files: 1
Image Reference: 134265 / 21868
Format and Version: PDF 1.2
Part Number: 1
Size (KB): 346
Number of Pages: 1
Price (£): 2.00
Total Price (£): 2.00

If your Grandfather's name was Gustav Heiser you might like to purchase an image of the card but, perhaps more importantly, armed with his Regimental Number (G/45999) you would be in a much better position to talk to the Regimental museum.  I think they relocated fairly recently and probably need all the detail you can give them to be able to help you further.

Once you have his Battalion either from the museum or from the medal card you will be in a good position to find out more about his movements and actions with the Regiment - see http://www.1914-1918.net/msex.htm

And I think that "shopping list" constitutes the parts for a radio receiver (an amplified crystal set).  If he understood German he might have heard some very interesting things with the assembled device but I'm not sure that such intelligence-gathering was a regimental (or even divisional) responsibility.