If you could give your friends 3 seeds to grow......

[2 As and a B]

Thank you for this thread Catweazle. I think our toddler of a TT group could use your idea to generate some interest now that the growing season is almost upon us.

[contadino]

If you're allowed to count a pack of seeds as one...

Sorrel, Cima di Rapa, Quinoa

If you want stuff that'll just keep going...

Chard, Rhubarb, Courgette

For kids...

Some sort of big squash (like Cento Quintali), Strawberry, and a vine

For the future...

An almond nut, a carob nut, and an olive.

None of which are high maintenance.

Although my personal preferences would be...

A lemon pip - Fruit are edible, and a great ingredient for cleaning.
An almond - 3 years on you could get your first fruit. Good to graft onto, a carbo staple, can make almond milk and flour
A squash - something like a butternut. Stores forever, not so big that once opened half goes off, easy to save seeds, trouble-free growing.

[Mark]

I've had an allotment for 4 years, so am just about starting to get the hang of it now.......

Not all seeds, but for instant results with absolute minimum effort, I'd go for:
radish
mint
rhubarb

For slightly more effort, I'd choose:
spuds
leeks
kale
All staple foods and easy to grow. You can store potatoes over the winter. With leeks and kale, you can leave them in the ground for months, extending their period of availability.

Somebody else has suggested blackberries, which would be another very 'low effort' choice, but the brambles would make the garden look untidy (if they're bothered about that kind of thing). Also, they're easy enough to forage, if they live anywhere within striking distance of a hedgerow.

[DominicJ]

I have a thornless bramble, on a fence it looks fine.

I dont personaly see subsistance farming as being possible or required any time soon, so would suggest low effort/high pay off.
Herbs and fruit.

I've got Sage, Corriander, Basil and Parsley planted, along with my fruit.
Very little effort required for lots of reward.