A Very nice adaptation of the Army Field Manual on Survival. Try these plant substitutes for coffee.
Most pollens are edible, they are normally too fiddly to harvest.
This thing is HUGE, so get your coffee before clicking this link. Pretty fast database, though. Several microscopic marine algae are notoriously poisonous to hapless humans who consume them in shellfish. In fact, many of them are sickening or deadly. Exercise extreme caution when picking wild mushrooms, and if you're not certain about what you're picking, don't do it .