I’ve used a Rukus as a daily daypack for the past eight months and agree with you about the usefulness of the pack is due to its shape that allows the pack to expand to store a huge amount of gear, more than I expected. Certainly large enough for an UL overnight trip or for loading up as carry-on luggage.

The only real negative I have with the Rukus is some of the minor design details and workmanship: the seams that go across the shoulder straps are coming undone, the drawstring eyelet is coming loose as it is not reinforced with an extra layer of fabric, the binding of the internal seams stopping just before the drawstring seems to catch on things when they are stuffed into the pack. The internal zip pocket could be a littler larger too.

Hopefully a version 2 of the Rukus is released.

The Marmot looks similar to the GG Type II. A nice design I find. The Rukus has really shined as carry-on luggage. I think it will work well for your Scotland trip!

The other light daypack I really like, is the Marmot Kompressor ultralight. We got two of these for use as daypacks on backpack hunting trips, they have worked really well – comfortable, light, and can haul a surprising amount of gear – emergency kit, raingear, warm gear, hunting knives, ropes and game bags, etc. The main reason I bought them was that they came in a hunting-orange colour, but would buy again in any colour..