Bargain of the Century! Deal of the Decade! Call it what you will, but Double-deckers are on sale in Tescos (none in East London though, I bought them all). £1 for a four-pack. For the mathematically challenged that's 25p ($0.40) per bar, approximately a third what petrol stations charge for them. This is incredible, truly mind-blowing. You can now eat three times as many Double-deckers for the same money. Or to put it another way, go birding for three times as many days.
For those that don't know, Double-deckers are a thing of beauty. A layered chocolate bar, rice-krispy style stuff on the bottom, nougat on the top, with the whole thing wrapped up in milk chocolate. Mmmmm mmmmm. 60g and 275 calories of bird-finding goodness. Cadbury's first introduced them in 1976, the year after I was born, perhaps sensing that a new era was dawning. It is basically the only chocolate bar that I have ever eaten - my parents used to buzz them up when I was little and feed them to me with a spoon.
These days, they are strictly seasonal, like vegetables. Cadbury's produce them in late April and May, and then again in September and October, to coincide with migration season. Outside of these times you'll be lucky to find them, particularly inland, though coastal locations may see occasional over-stocking. They are scientifically proven* to sharpen birders' eyesight, and increase the sensitivity of their hearing, as well as allowing them to absorb Duivendijk at a rate of up to three-pages a minute, rather than the standard two pages per month. As you can see, pretty potent.
Every September, in anticipation of the rarity-fest that is to come, I make sure to stock up, so imagine my delight when I found them on special offer. I did not hold back, and now have twelve bars, plus one left over from May - the spring was fairly poor. This will allow me to go birding for three entire weekends plus my Shetland trip. You must only consume one per day, any more and you may start to talk about BBRC rarities in your sleep. When in the course of the day you eat it is of course entirely up to you, though personally I tend to break it out in very promising locations, or perhaps when a rare bird is being skulky and we need to get a move on. This is known as "working the magic", and usually results in the previously elusive bird seeking the highest possible perch and calling its head off a short time after consumption.
So, if you're heading to the coast this autumn, or to some remote archipelago, or perhaps just birding the patch, make you sure have an emergency Double-decker stashed away somewhere - you just never know when you'll need its magic.
* ESSO/BTO study. Kind of.