2-3lbs of colonized spiral-cut hardwood dowel plugs. These are used to grow mushrooms in living trees (non destructive species) or old wooden logs.
All you need is a 1/4 inch drill bit - identify the hard wood log of choice and make a series of holes in the log, plugging each with a colonized dowel and covering with wax.
Logs inoculated with mushroom plugs will fruit mushrooms for many many years as the fungus breaks down the log.
Trees inoculated with plugs will gain significant boosts to nutrient uptake and immune systems in a symbiotic relationship. When the tree dies the fungus will become dominant and break down the now dead tree.