What we can't do is guarantee a fun and frivolous time that absolutely won't make you want to gnaw your own leg of in an attempt to get out of it. What we can do, is suggest a list of things to pack which might come in handy.
1 An extra pair of tights. As grown-up, responsible members of the community, there is a high likelihood that the in-laws will be dog owners - we're generalising, obviously, but if they can raise children, then a pet's a doddle.
The issue is that Bramble and Bracken take advantage of their owners' newly-found relaxed attitude now the offspring have flown the nest and will dive-bomb guests upon entry to the house. Within minutes, any dark clothing will appear Wookie-like.
Unfortunately, there is no such thing as fur-repelling hosiery on the market just now, but in terms of hard-wearing, good-quality tights that will survive a spin cycle or eight, try Wolford or Bebaroque for those who prefer a fancier leg.
2 Appropriate nightwear. The use of appropriate obviously depends on the kind of attitudes held by your in-laws. If they're a couple of liberal Larrys, then great, but generally, wafting down the stairs for Sunday breakfast in something silky (for either gender) may result in having your porridge laced with arsenic.
If we're considering nightwear as a spectrum, with Age Concern at one end and Agent Provocateur at the other, we'd advise hovering around the middle mark. Calvin Klein does good pyjama sets for both ladies and gents, plus its line of dressing gowns nicely combines functional and stylish elements (think minimalist form and colourways dark enough for concealing spilt egg yolk).
3 A scarf you no longer wear for when/if the following conversation arises:
Mum: Oh, that's a lovely scarf. Where's that from?
You: It's COS, two seasons ago. Do you like it?
Mum: Yes, it's really nice.
You: You can have it. It suits you better anyway.
A sneaky bribe and it saves a charity shop run all in one. Sterling effort.
4 A nice frock/smart slacks. Chances are you'll be going out to dinner somewhere local for everyone to bond over a basket meal. Plus, in-laws (and your own parents) assume that you live some sort of impoverished and sinful existence in the city now that you've left home, surviving only on pot noodles and new kinds of energy juice that the Daily Mail has proved causes rickets, three types of cancer and adult acne.
Levis do good, dark gents' jeans (no stonewash round these parts, thanks) that are also water-resistant in case their wearer gets emotional remembering they're spending Saturday night eating in Brewers Fayre. For the ladies, we recommend this dress from Whistles - which is coincidentally the perfect colour for blending into a scampi supper.
5 A roll neck jumper. People's parents love Doing Stuff. It's just a fact of life. If you're not a fan of Doing Stuff, and prefer to hang out in bed for an entire Sunday surfacing only to prepare Man v Food type snacks, then this is where you might come a cropper. For the uninitiated, Doing Stuff often involves the following elements: cold, rain, walking, waiting, and car journeys. Allow no margin for error by packing a warm layer that can be taken on or off quickly depending on the circumstance, and the roll neck eliminates the need for a scarf (clever, right? You can thank us later). Think of this as training to one day becoming a fully fledged day-tripper. Take your new found knowledge and responsibility (plus a packed lunch), and run with it.