Surely any sort of cake/margarita/chicken dish which does - or doesn't - require a bit of zing! That's how I feel about it anyway...Left over lemons make a great addition to a cocktails because both the juice and zest adds a nice zip to a drink. Equally, lemon zest can be grated into a cake mix.
On another note, spare lemon juice is a fantastic cleanser for the skin. See my scrub on Healthy Hints and see how I use it to make a natural exfoliant. Hope this helps.
I only use lemon to drizzle over grilled fish fillets, prawn cutlets, veal schnitzel. IF I have some left, just leave it in cool bin, wrapped tightly in plastic bag. It'll last for awhile.
Also love it just sliced & pop into VERY cold glass of water! On a hot day, that's just heaven to drink!
Leftover lemon, u can use the juice for Lemon rice, two tbl spoon of juice in a glass of warm water and add pinch of salt and drink, it is good for health. after and skinn u can cut pieces and add to your dish washing soap.its natural. (i will send the lemon rice recipe later)
Slice it up, place in M/W jug of water, place in M/W, & let it boil for a few minutes, long enough for condensation to form on surfaces. Take out jug, & wipe surfaces over. Lovely sparkling clean appliance!
Put lemon remainders' into compost. You could drink the boiled water, once cooled!
I just keep the other 1/2 of the lemon I don't need at the time, in the fridge until another recipes calls for, 'The juice of 1/2 a lemon.' Lemons are so expensive now, I don't like to waste them. (Jan '19.)