The question I most often ask when I'm buying a plant is: does it last forever? I've never been a fan of stuff that dies after one season, or disappears in winter then resurfaces the following year just when you've planted something else in the gap.
I once planted a whole heap of perennials in one plot and when they died back in winter, I did a quick redesign in a completely different look. So I was furious when bright flowers appeared in late spring and wrecked my monochromatic combination of lichen-covered rocks, silver astelias, blue grasses and grey lamium groundcover.
With the exception of a silk tree (and you can't not have a silk tree), all of our trees and shrubs are evergreen. Vegetables, though, are a different kettle of fish, if you'll excuse the mixed metaphor. Most of those I grow are temporary visitors, lasting the season if they're not taken out by fungus diseases, bronze beetles, white butterflies, slugs, snails and cats.
Happily, I read something the other day on how to prolong the usefulness of certain vegetables and herbs. I'm trying it, mainly because it sounds like fun. If you have kids, they'll probably enjoy this too, and it may even cultivate their interest in real gardening that you can put to good use when you need a hand.
Carrot greens
The ends of carrots that you usually chop off and throw out will grow carrot greens if you put them in a dish of water. Put them on a sunny windowsill and, once they've grown, use the carrot tops as garnish or in salads. Carrot foliage is really pretty, so it's no hardship to have it on your kitchen windowsill. Far better that than the Landscaper's soil-encrusted transistor radio which decorates ours.
Garlic
Don't throw away those sad bits of garlic that have sprouted in the vegetable bin. Put them in a jar with water and grow garlic sprouts. The sprouts are milder than cloves so are good in salads, add them to pasta sauces or use as a garnish.
Basil
My basil's gone badly to seed so I'm giving this a go. Put a few basil clippings with 10cm stems in a glass of water and put it in direct sunlight. When the roots are about 5cm long, plant in pots.
Shallots (Or scallions or green onions)
Now this is great if you've a short attention span. You can regrow a full shallot from the scraps of an old one. Leave about an inch attached to the roots and put in a small glass with a little water. In a few days, you'll have all new ones.
Romaine lettuce
If you have a stem from a head of romaine lettuce that's still intact, put the stump in a bowl with about 2cm of water and add it to the windowsill. You should see new leaves in about a fortnight. Bok choy will do it, too. Put the root end in water in a well-lit spot, and in a couple of weeks, transplant in a pot of soil. In no time, you'll have a whole new head.