Those of you hate Marmite - look away now!
I always struggle with the awkward shape of the Marmite jars (I love them, but they're difficult) when it comes to those last iddy biddy little bits all round the inside of the jar, but now I have a neat little frugal tip that will use every last bit of Marmite in the jar.
When you have used all the Marmite you can scrape or spoon out of the jar and given up, boil some water and fill the jar, screw the lid back on and leave to stand for a bit (half an hour should be enough). Shake gently (be careful as I've discovered to my cost that Marmite jar lids are not always water-tight) and you have a quantity of stock (depending on jar size) which you can use in gravy, soups and stews or as a nice warming winter drink - but then you may have to reheat it in a mug!
Freeze as you would normally freeze soup if you can't use it straight away.