What do you use/have?
Fancy a rucksack type cabin bag to enable me to wrestle with the bike bag.

This looks good but it says it’s just slightly too big?
https://www.alpkit.com/products/drydock-50
I have a big NF one for hold luggage duties.

40L mountain equipment one. that fits in fine.

NF do a 42L which is also probably fine for cabin baggage

Edit:
Various here http://www.cotswoldoutdoor.com/equipment/rucksacks/duffles

I use an Osprey Farpoint 40 at the moment – smart enough for work use but with a zip away rucksack harness.

40L for cabin baggage? I feel guilty with my 28L Vaude rucksack

Slightly off topic but depending on the use bag, hold and hand luggage on the trolley pull the bike bag on its wheels. Works heaps better. Was looking at the evoc hand luggage for weight mostly.

I have a Gelert rip off of those NF ones.
Same sort of thing as this Karrimor
http://www.gelert.com/karrimor-40l-duffle-bag-794079?colcode=79407903

Lots cheaper than NF or Mountain Equip.
The Alpkit one looks better though. I find the covered zip a PITA

I have the alpkit one, a journey to Berlin then to Lisbon and a couple to London on the train, my impressions are –

Will fit into hand luggage ifno t bulging allow some squish space
The straps for the rucksack are comfortable and fit flushfor the train journey.
It is big enough for me for a relative long journeys.
Not adrybag but very weather resistant
Pretty well made but exceptional for the cash

Downers
When on your back it is big
You will be heckled by street buskers
Reasonably weighty when empty

I would recommend but daughter has an arcxetry duffel thing and that is lighter and slightly nicer.

I just use my work laptop rucksack thing…

Lowe Alpine TT Carry On 40

Has done lots of flights and works in a most excellent way

I travel hand luggage only, I’ve done 10 days combined work (need laptop and bits plus had to wear suits) and personal.