There are several ways to perform urban foraging. The right balance to find is not to spend too much time looking for an item. A lot of things can be found for free, but you often have either to be lucky, or to spend a lot of time looking for it. Sometimes, paying a few euros can help save a lot of time.
I frequently update an Excel file where I list all of the materials & objects I need for current and forthcoming projects. I try to have most of it in mind, and always take a copy with me when I am going to second-hand shops.
I made most of my seedling pots out of bottles, cans and diverse containers recovered from FoAM's garbage bin. Before foraging any further, making the most of the resources at hand is the most efficient strategy.
Up till now, I foraged several kind of products from the street: wood pallets, cardboard, plastic bottles, cans, eggboxes, styrofoam, glass windows…
There are so many cool stuff that people dump that I could basically transform FoAM into a recycling storage space. I try to moderate my collection, and therefore focus either on rare items (like glass windows) or things I am going to use straight away (plastic bottles for my self-watering experiments).
However, I often have transport issues. During a hike around the city, I found very nice glass windows, or even a 2 meters mirror. As I was more than one hour walk from FoAM, I could not carry these heavy items all the way back to the studio with my bare hands. Maybe should I always take my 50 L backpack with me when I walk around ? It would not allow me to carry everything, but it may already allow me to carry more small items if needed.
There are several online initiatives to avoid dumping out useful stuff. Amongst them are several groups to which you can sign up. I subscribed to two groups: Freecycle, and Bxl à récup (Facebook). On these groups, people post things they are planning to dump and propose them for free. Whenever I am interested by a product posted there, I just have to reply back to the post and that is it.
It is interesting to keep an eye on these sources. Althoug, you can post requests for specific objects too, they only very rarely attract relevant replies. This is their main drawback: you have to wait for luck to operate, and make the object you need appear. Moreover, the most valuable the object, the quicker it will be taken by members of the group: you have to check the list very frequently !
I have not obtained anything I needed from this channel yet.
For a few euros, I could get essential products difficult to find on “free” channels: big mirrors to reflect light on garden plants, bassins to collect grey waste water for the plants, a glass microwave plate forming the basis of a solar oven, grids on which I will be able to dry fruits and vegetables…