Plastic - would prefer not to use it, but sometimes it is all there is to use. Part of the problem with gardening on an extreme budget is that the good-quality materials are often out of reach. So I try to choose foam containers that are not too degraded, and while I grow some food crops in them, they are the ones like watercress, miner's lettuce and regular lettuce that have a very short growing time and shallow roots. Ceramic containers would be nicer, but they can cost hundreds of dollars, which I, and many others, can't afford. So apart from what is in the actual garden (mostly perennial crops, fruit trees and root crops), and the water plants growing in foam boxes, I have stuff like water lilies, lotuses, Typha, weaving rushes, nardoo and water irises growing in old bathtubs and an old laboratory sink. Our community garden grows water lilies in a recycled spa tub, and uses several old fridges for worm farms. Works for us.
The one that really worries me is the use of treated timber for making raised beds. Recycling wood such as vineyard posts for anything except raising structures from the ground is a bad idea - many of the anti rot and anti termite chemicals used on such things are very poisonous, and can leach into the soil.
