I used to cook from scratch a lot more than I do now. It's a combination of laziness, lack of time, and lack of will that keeps me from doing it more often. Most of the time, I'll buy something fresh and it ends up going off before I can summon the will to cook it.
I've found a few items that are sort of transitional between prepackaged and from-scratch. These are the things I fall back on to keep my food a little bit fresher without wasting money on ingredients that go off and saving time on cooking:
Sainsbury's frozen chopped spinach:
I love this stuff. I use it almost exclusively for tofu scrambles, though I've used it for other things as well. It lets me get some green in my food without spending stupid amounts of money on things that go wilted and slimy in a couple of days.
Karyatis roasted red peppers:
Do you know how much red peppers cost? Those fools are expensive - about 80p each for fresh, conventionally grown red peppers. I rarely use fresh red peppers anyway, and this jar is £2.39 for 4-5 roasted peppers. And they last a lot longer. So really, that's just good sense. I use these peppers in my Almost Zatarain's Red Beans and Rice.
Frozen chopped onions and minced garlic:
You'd think most people would be able to use onions before they go off because they last so long. Not me. I don't even know how many rotten onions I've thrown out because I just couldn't bother using them when I actually remembered I had them. And I've had some bad luck with garlic sprouting before I get a chance to use it (I mean, within a week - I need to remember to stop buying garlic from Tesco). I usually get frozen onions and garlic (and occasionally shallots) from Waitrose because they often have them on special. It seems like such a lazy thing to use until you realise that I just wouldn't use them at all if I had to chop them myself (well, and remember to have them on hand).
Sainsbury's ready-rolled light puff pastry:
Every once in a while, I want a savoury (or sweet) pie, but I don't want to faff with making crust. Enter the pre-made, pre-rolled crust. Yes sir. I've used this to make porkless pie and chocolate parcels and probably some other stuff that I can't remember. This will feature at some point this month - I think I might make another bean-based pie or a tofu-based savoury pie.
What are your favourite convenience ingredients?