Don't quote me on this, but I believe that is the 1% ABV increase "add-on" that you can request in any of AHB's kits. I always pass on the 1% increase b/c I just don't like the idea of adding plain ol' sugar to my extract recipes, so I can't guarentee it.
Either way, I'm guessing it is mostly just corn sugar and some maltodextrin, but the only way you will figure out the proportion is probably by asking them (if they are willing to divulge).
Either way, it is not necessary IMO for any recipe. You could brew the lawnmower ale without that and it would be just fine (maybe better b/c all malt?). For a lawnmower ale, I'm not quite sure why you would want to increase ABV anyway; it's supposed to be an easy drinker...