When dad used to take me, as a small child, to the allotments to pick all the soft fruit he used to ask me to whistle. It took me a while to cotton on.
When I used to take my son to toddler group (many moons ago) I started up a money off voucher box. All parents would cut out any money saving vouchers in mags or newspapers and drop them in the box for others to use and look through for any they needed. It had to be checked regular for out of date vouchers though, but some parents used to scramble for certain vouchers