Yes, that strikes me as a fair description too. I've only done a few walks and cycles on Lleyn so far, but it's definitely got potential.
A lot of the cycling would be on quiet lanes. But at the northern end of the peninsula there's an excellent 12.5 mile cycleway - Lon Eifion Cycleway - which runs from Caernarfon inland to Bryncir, with good views of some of Snowdonia's hills. I used it on a tour last autumn - traffic-free, good surface, a few gates along the way but they're wide and "easy-open" so I don't think they'd be a problem with a trailer.
For walking the coast path is the obvious starting point, and tbh I reckon you stand more chance of finding the paths existing on the ground than you might with some of the other footpaths marked on the OS map.
There's a Cicerone guide - "Lleyn Peninsula Coastal Path - A Walking & Cycle Touring Guide" - which describes the coast path for both activities. It's divided into fairly short sections so could give some ideas for out-and-back routes or sections to look for a circular return (or possibly link by bus if walking).
Other than the walking and cycling, you'll have a choice of decent beaches, a few nice little villages such as Criccieth with its castle, and if you head as far as Porthmadog a choice of two narrow-gauge railways, the Ffestiniog Railway (to Blaenau Ffestiniog ), and the Welsh Highland Railway to Caernarfon via Beddgelert. Actually, either of those gives opportunities to link a train trip with a linear walk.
As for the supplementary question of "any other recommendations for an emergency winter kit for the car"...
I tend to put together a bag that stays in the car all winter. Among the contents (and this assumes I'll have a decent coat, hat and gloves with me anyway, and add food and drink if the journey warrants it) are:
Aspen 4T is a very pure form of petrol and can certainly be used in a Whisperlite (I use it in my Optimus Nova).
I've never used panel wipe myself. I'm pretty sure from discussions on here that it's suitable in principle. If there's an issue it might be (by all means someone correct me) that there are different versions of panel wipe, some of which have a different composition or additives that might not be so good for a stove (???)