need luggage/packing tips for fast paced tour travel

hi guys! i’m doing a contiki tour next february (the european discovery tour). its 6 western european countries in 2 weeks, so there’s going to be a lot of transport days, and i’m wondering if anybody has any tips for what the most convenient checked baggage option is? my head is sort of messy and contradictory right now because i’ve never done any sort of fast paced travel, but travelling around australia i found having a suitcase with no outer pockets super annoying because i would have to open the entire bag just to pull out like a charger or underwear or something, however im concerned that the soft shell bags with outer pockets leave my luggage more vulnerable with handling/more difficult to lock. im also curious to know if a wheeled suitcase, a backpack or a hybrid bag is more convenient? my checked baggage limit is 25kg but im planning to pack quite light because im travelling from summer in australia to winter in europe which means i will definitely need to get some warmer clothes while im over there lol, as well as just buying general trinkets.

some other questions i also have:
1. is there anything specific you guys did with your dirty laundry while travelling between laundromats? or should i just shove it in a plastic bag and put it in with the rest of my luggage? i’m honestly not sure what the laundry situation is going to be like there at all lol

1. is there anything that people don’t think of to bring on these trips that you wish you knew about? i’m travelling from adelaide australia to london with a 7 hour layover in kuala lumpur, which is like a 38 hour flight total and have no idea what i should bring for plane comfort or just general convenience and comfort while i’m over there. i will also be staying in triple share room hostels.

i think i overthink this stuff a lot lol, whatever is convenient and worked for you guys is fine and im not too concerned about the structural integrity of my luggage if that’s an unnecessary concern, i just have no experience to determine whether it is unnecessary or not haha. thanks so much!