well done all of you.....not being a smoker, I probably have no idea what you are going through although I have observed others giving up over the years and have deep respect for your self control.
As a well earned reward why don't you put the money you would have spent in a jar and after say a week/month/year spend it on something for your allotment that you would otherwise wouldn't have bought due to it's expense or extravagance. Maybe a greenhouse heater, replacement wheelbarrow, chair,lawnmower,strimmer,shed, fruit bush,secateurs....and then you can be reminded on a regular basis how well you have done for years to come (as well as get even more pleasure from your fruit and veg growing!) Keep up the good work.