I so would love to have a bit more land - more land would give me a bit more room to plant all the trees and plants that I want to... That might mean having a couple of people looking after them all for me.
I have some plants like white willow - the bark has been known from ancient times to be useful as a medicine. There are plenty of other plants which I could find very useful...
I've been looking to find rubber trees, but I think I'd need plenty of land, and not have them too close to any house - apparently, the roots can be very invasive. Would be useful to have, though - a source of latex rubber without having to depend on oil deposits, pumps, refining equipment.
If nature is capable of doing most of the work for you, you should let it.
Eucalyptus grandii seems to be a very useful source of wood - grows very quickly, can be coppiced (ie cut down, and will regrow from the stump). Makes forestry a better activity - you can cut down and not have to replant manually - saves precious time, energy, and resources.
I will admit that I'm looking at scenarios where the environment is not completely wiped out when SHTF - but if the world freezes over, it's going to take much more resources than I currently have access to. Not that that type of scenario would be impossible to deal with, but I'd want to go underground, would need geothermal power, need a significant aquaponic system just for air, let alone food. Not an unsolvable problem, but we can only do as much as we are able.
I definitely requires more land... And I can't quite just keep plants in pots, wait until TEOTWAWKI, and plant them out into the land around me, can I? Actually, not grandii - apparently, it can grow seven metres in its first year. Okay, anything that produces viable seeds would be okay to use, but I wouldn't want to have to graft post-SHTF just to have a viable food supply, or water a hundred potted plants pre-SHTF.
I'm also trying to grow some cotton - having moderate success doing so, though I've not sprayed it against pests, so I am not sure whether the raw cotton is getting eaten before it's ready. I have to plant some pyrethrum out - a very good insecticide. Add in there various dye plants, and you can see potentials. The whole of Organic Chemistry as a field of study and industry started because of the want of large quantities of dyes.
There are more plants out there that have uses PSHTF than just the ones that you can eat.