1. Park by the old bridge outside Llanelltyd and go up through the woods W of the village to reach the New Precipice Walk. Use that as your access to and from the obvious horseshoe to Y Garn (629m). Great views over to Cadair, along the Mawddach estuary and into the Rhinogs.
2. On the S side of the Mawddach estuary, park up by Llynnau Cregennen and take the footpath E to Kings YH, then climb up to the campsite and the Pony Path to Cadair. But when you reach the col, don't turn E for the summit, head W along the superb grassy ridge towards the sea. It stays around 600m much of the way. After Trawsfynydd descend to the forest and the old track leading NE back towards your starting point. You can see some of the terrain on the early and later stages of this trip report.
3. The southern end of the Rhinog ridge - a bit higher, reaching 750m on Diffws, and sharing some of the ridge with Marcus' suggestion. You can park a car by the phone box at Llechfraith. There are several possible ways up Diffws depending on your preference. There's the track up the forested valley to the east that runs N or the ridge over Mynydd cwm Mynach, both sharing the final quite steep, rough pull up to the summit. Or the gentler ridge of Braich, which could otherwise be your descent. I've never tried the ridge directly up Craig Aderyn but I think it should go. A descent can follow the ridge all the way W over Llawlech to the Bwlch and then a good track leads back to Llechfraith.
I always carry everything electrical in hand luggage, and that's typically a camera, gps unit(Garmin), mobile phone and torch, plus assorted spare batteries and chargers. I do wonder what it looks like on the scanner but I've only ever been stopped once (in 20+ flights) and that was no issue once I opened the bag and let them see the items.
I carry a lighter for my stove in hand luggage too. No stove fuel anywhere of course.
Anything sharp, even a tiny mini-leatherman, goes in the hold, as do walking poles.
I tend to put any liquids / creams etc in the hold for simplicity, but otherwise be aware of the small quantities allowed in hand luggage provided they're in a regulation clear plastic bag as you go through security - on my outward flight I take some of my contact lens supplies that way just in case my hold luggage is delayed at all.
An empty water bottle or bladder won't be an issue in hand luggage. Of course once you're through security you can fill the bottle if there's a drinking fountain, or buy bottled water to take on the flight, or "(not)duty free" drink which must stay sealed (if you're on a multi-stage flight make sure the shop put it in a sealed bag for you or else the next airport's security will have it off you!)
Be relaxed and civil to the staff (even if you're feeling naffed off with the process), don't joke, answer any questions and just treat it very matter-of-factly if they do decide to inspect your stuff, and it should all be fine.
A bit of googling reveals it's the remains of the brig Athena. The ship ran into trouble during a winter storm in December 1852, while sailing from Alexandria to Liverpool. All 14 crew members were rescued.
Surely everyone remembers the Hungarian phrease book? ("Drop your panties, Sir William, I cannot wait 'til lunchtime.")
Whereas nobody expects the Spanish Inquisition...
Edit:Ah, MoS beat me to it while I was brushing up my Hungarian.