Scans_Daily

Probably repeating what you already know, but the banana bit is not totally random, it's a reference to an earlier scene where the Doctor inspects Jack's gun;

Nine: Sonic blaster, 51st century. Weapon Factories of Villengard?
Jack: You've been to the factories?
Nine: Once.
Jack: Well, they gone now. Destroyed. The main reactor went critical. Vapourised the lot.
Nine: Like I said... once. There's a banana grove there, now. I like bananas. Bananas are good

I think the implication is that Jack will use the blaster as a weapon, but The Doctor will only use it as a tool while Jack can get himself some potassium, but yeah, not their clearest moment.