I cook about 90% of my meals from scratch (no, I don't make my own sausages, bake my own bread, make my own pasta or smoke my own salmon but you know what I mean).
Generally I think it tastes loads better but since having kids I have resorted to microwave rice, pre-made mashed potato, pre-prepared meat and potatoes on the odd occasion.
I've even made my own hummous in the past (not particularly worth it except if weaning) and guacamole (totally worth it)
However, I've always used some stuff from jars, like:
Dolmio bolognese sauce (always thought it was full of crap but it's not, only quite sugary)
Sacla pesto (the chargrilled aubergine one is amazing)
Ambrosia custard/rice pudding (I did make my own custard when I lived abroad and it was lush, but no time for that now)
Stuffing from a packet
Bisto gravy (would love to make my own gravy one day)
Spice Tailor curry kits
The odd stir-fry sauce although my own one is awesome, just a bit time-consuming
That's about it, I think, but would be interested in other shortcuts that work well!