i've just bought some "clif shot bloks". one pack contains 6 "bloks". the recommended "dosage" on the packet is between 3 and 6 bloks per hour of exercise, but i think that might be a bit on the high side for me, so i'm going to experiment on this weekend's 15mi run.
the whole packet (6 bloks) contains 48g carbs, 0.14g sodium and 1/2 shot caffeine (no specific mg measurment for that). Seems a bit low on sodium for the price of £2.25 a packet. Much cheaper to make up your own drink solution, with some dioraltye and orange cordial, and sip that along with water provided on the course, but i'll try these out anyway, see how they fare.