Ha! When I saw the title the first thing that came to mind was cacti and those long, thorny plants. I guess that goes to show where my mind's at.
Unless you're willing to do yardwork, fruit trees cost a lot in terms of maintainence, trimming costs, etc. If s(does)htf, it makes your house a target.
On the plus side, sharing fruit with neighbors builds a lot of good will and they may come to your aid if shtf, but unless they have the prepper mentality at best they may just expect you to feed them. Worse, they'll mob you and take everything. Maybe you have a dog, but who's to say they won't eat your dog as well?
Small garden plot, or planters are probably a better choice but unless you're dedicating a lot of time and square footage, your output may not be cost-effective, particularly if you don't can foods. Figure out what you spend monthly on fruit and veg and compare it to what it will cost to plant a garden that will give you the same yield. Factor in your time at whatever hourly rate you are comfortable with and if the numbers make sense, do it. If the numbers don't make sense, take the money you would have spent and add it to your monthly gun/ammo fund.