Excellent thread OP! Here's mine -
Do a bulk order of gorgeous cards early January from Whistlefish so they work out £1 each then at the end of a month get all cards written for the next month with a post date on the back bottom corner of envelope so they go out on time
Like a pp keep a list on my phone if gifts we've been giving to avoid duplication
Also on my phone keep a note of what I have stored in my various huge bags in the loft. That way when I send DH up to get something I can direct him to the right place. Although currently all our lift contents are stored all over the house having had to empty it at the start of this year having discovered we have a fucking rat. And it's still not gone despite x 2 pest control bods being called in and it's entry point blocked in. Waiting for the bugger to die and it's horrible. Just want my bloody loft back. Anyway I digress, apologies
Passports - strip of washi tape on the back with our first name sharpied on. Much easier to match up with boarding cards
Shall think of more ...