This may surprise some, but the UK public water system provides drinkable water throughout the British Isles.
Things are perhaps different in America?

There’s a chain store called Halfords. It’s an odd combination (to me, at least) of auto parts and bicycles. Their website shows the 4 pack of Campingaz cans. Maybe there’s one near your hostel.

The one I mentioned was 4 miles from the hostel I stay at in London was a Halfords, website says available one hour after purchase at that store.

Thanks.

I don't know if Dan set up the forum to be considerate of the members' time when he renewed the forum several years ago, or whether he chose software for being human-friendly, but either way he gets the credit.

Especially, I must say, compared to Facebook, which every time I want to log in to my group for other writers, Indie Authors International, sends me on a runaround which can consume anything from twenty minutes to twenty hours of my time, and does it several times a day. You'd really think that Meta, with all its billions and umpteen thousands programmers, would do better than a single volunteer, but you'd be wrong. Signing in to the Thorn Forum by contrast to Facebook is a two-click operation and then you're in.

Hurrah for simplicity! Thanks, Dan.

There’s a chain store called Halfords. It’s an odd combination (to me, at least) of auto parts and bicycles. Their website shows the 4 pack of Campingaz cans. Maybe there’s one near your hostel.

Good idea; Halfords. I should have flagged that up for you. Yes, a little odd perhaps since much of their gear is for the motorist but certainly most branches have cycle items and I have seen gas canisters. and camping items.

Ph, thanks.

I wrote all of the text below before I saw your post.  Islands, Arran is a strong maybe but I have not planned on any others at this time.  And probably will not add any more to my plans.  If I really like this trip, I might have to come back.

***

RonS and Matt2matt2002, thanks.

In one of my google searches, Ember popped up.  I looked at their website for enough time (about 5 minutes) to realize that I should put their info into my records that I take with me on my phone as a contingency.  Was unaware of City Link, thanks for that.  I added City Link website to my notes.  I am putting  a text file of my notes on info that I might want to have with me later on my phone, the two bus lines are added to that. 

Nice to know that a full campsite might not be really full.  A few times in my travels, I have discovered that full really meant full.

For the hostels that I have not already made a reservation at, I am now thinking I should make a reservation 24 hours in advance, if not more. 

And, if all else fails, I do not need to panic:
https://www.visitscotland.com/accommodation/caravan-camping/wild-camping
https://www.wildernessscotland.com/blog/wild-camping-scotland-best-practice/

I will bring a Steripen in case I need to treat water.  I bought it for my Iceland trip, never needed it.

I wasted two hours yesterday.  As a double check I looked at the Decathlon store website again.  For the butane I was going to buy it said not available for pickup at store, not available for ship to home.  Searched a bunch of other store websites, found a store where I could buy butane four miles from the London hostel.  Then took one last look at the Decathlon website again, clicked in a different spot and it said it was in stock at that store.  So, that was two hours wasted on the internet that I will never get back.  I plan to get a four pack of the long skinny type Campingaz CP250 fuel canisters, that would be 880 grams.  My Iceland trip, I used 35 grams per day.  Thus, 880 grams gives me roughly 25 days of fuel.  That should be pretty close to what I need, assuming I use no fuel when at a hostel.  If it starts to look like I am running low, I can look for a canister in Fort William, there are camping gear stores there.  And I can scrimp on fuel use if I have to, when backpacking I average about 28 grams per day, even though I plan for 35 grams per day.

Sometimes my preplanning can be a bit too thorough.  But my tour two years ago where I assumed campgrounds and motels on my map were accurate, in one day I found two campgrounds that were gone, one motel had been torn down two years earlier, and the other motel had a closed sign.  All in one day that became a 14 hour ride.  Later on that trip I arrived at a campground, it had closed years earlier and been replaced by a hoard or rental cottages.  So, this trip I am being a bit more thorough in looking at the websites for campgrounds, etc., to make sure that they exist.  One campsite I plan to stay at on this trip, their website said copyright 2018, so I was about to cancel that one from my plans, but then I saw they had posted their 2026 prices.  Thus, they had not closed in 2018.

Now, I need to focus more on getting in shape.  This past Wednesday, rode my Nomad Mk II on a route that is mostly gravel trail with some hills for 54 miles, I really need to focus more on longer distances in my remaining weeks.