The attached specifications have nice descriptions, including sizes of 08 packs and haversacks.

For 1914 pattern equipment, see http://www.karkeeweb.com/1914main.html.

More photos of back packs and haversacks. Having made miniatures of all of these types I've found you can't have too many images.

RE = Royal Engineer

Another web site, www.sofmilitary.co.uk, Soldier of Fortune Militaria indicates that the 1908 and 1914 haversacks were 350mm x 250mm x 90mm or 13.8 inches by 9.8 inches by 3.5 inches in size, a bit different than Karkeeweb.

As with most officer equipment and uniforms, officer haversacks were private purchase normally. All were identified as 1914 haversacks and an officer version of the 1908 design was not mentioned. The posted examples were found on the Soldier of Fortune Militaria and the www.dbg militaria.co.uk, DBG Militaria, web sites. The relative size of these haversacks was 12 inches by 12 inches by 4 inches - so a bit smaller than the other ranks haversacks.