The classic Weber barbecue is equipped with an aluminium pan for collecting the ash. More expensive models have an ash can that goes a bit longer between empties.
This mod uses an illy bulk coffee can to collect the ash and goes even longer between empties.
Where and how you source the barbecue is up to you.
For the coffee can you can either wait around outside a coffee house until one gets thrown out, or you can go into the coffee house, make your needs known to the proprietor, and buy a few coffees to help empty the can. (BTW: Make sure that the coffee house serves illy coffee!!)
Carefully, the metal is sharp, cut out the top (lid end) of the can with metal shears to make a bucket. Wear heavy work gloves and eye protection to protect yourself from the sharp metal.
Mount the can under the Weber kettle as in the photo. The original clips that held the aluminium tray can be reused to steady the top of the can. Support the bottom of the can with some scraps of wood or other suitable material.
Put some sand in the bottom of the can to line the bottom and to prevent heat getting to the wood support blocks.
Now, get on with your barbecue and enjoy. At least you won't have to empty the ash collector so often.