Well, loads of the mangoes are still green when they get to the supermarkts, so can believe that they come by boat, and are picked green. If the boat's refrigerated, loads of things could come by boat.
Bananas come by special shallow draft refrigerated 'Reefer' ships. They are transported in the perforated carboard boxes stacked on pallets you sometimes see in supermarkets and they are 'put to sleep' in a controlled and refrigerated atmosphere then a few days before docking the ship hold is pumped full of ethylene to ripen them.
Don't sweat too much about flowers coming by plane. I used to work for a company that flew gold bars plus orchids out of African airfields on freighter 747s. Don't ask - its heart of darkness stuff. The gold bars weigh a lot but take up little room and the orchids weigh a little but take up a lot of room. They still do the same today to optimise air freight space and weight.
The other fruit such as New Zealand apples comes in 40 foot shipping containers, by container ship. The containers are climate controlled to slow ripening.
I suspect, only fairly high value, short life fruit and veg is air freighted outside the UK season over long distances (e.g green beans from Africa).
Roses from Kenya are almost certainly air freighted.
An air freight configured 747-F has 140 tonne payload so probably would carry a cargo of roses stacked vertically in boxes on pallets in a climate controlled environment along with heavier freight that may well include gold and platinum picked up in South Africa on a short southern flight before flying the long return leg to the UK.