Hi TillySouth. I am writing this as I suffer jet lag after returning from a six week trip to UK. My biggest lesson from my trip is that past experience is not a good guide for what will work on the next trip.
In 2010 I travelled with my wife and for part of the trip with our adult daughter to Paris, Ireland, London then Europe totalling 12 weeks. What worked on that trip for my wife and myself on that trip was one checked suitcase, one carry on bag plus hand bag for my wife and a man bag for me. The man bag for me allowed me to keep essential supplies (like medication needed during flight and book) under my seat, no need to access the overhead locker during the flight. The 'carry on bag' carried the remaining essentials, like laptop, medication, allowed toiletries and a change of clothes in case checked bag goes missing. The 'carry on bag' was carried over the shoulder. When we were travelling on land, the 'man bag' was used for walking about, containing a warm top, camera and a few other bits an pieces. This bag was carried across the shoulder keeping both hands free, and the bag could be moved to the front of my body in crowds for better security. The 'carry on bag' was used as an overnight bag if we had a single night stop, avoiding the need to open the main suitcase. The single 'checked bag' only worked (i.e. kept within weight) because we posted home heaps of clothes and books we bought during our travels.
For the trip we have just done to Britain (we returned literally yesterday) none of the above worked. First, I took a wheeled 'carry on bag', which was much easier to handle. My wife took a shoulder carried 'carry on bag', but found it so uncomfortable she bought a four wheel bag. I took the same 'man bag' as the 2010 trip, but realised when we arrived I realised it would not fit my big SLR camera, it made it too heavy as well. So, I bought a small backpack, which worked rally well. My wife also bought a backpack, larger than mine because the protected (secure) shoulder bag was too heavy and too small, and that bag worked for her. We also took the same single suitcases for 'checked bags as for 2010. However, we realised that this resulted in the bags being too heavy despite being 10-kg under the allowed weight for checked bags. Being a bit "older" the bags were difficult to lift if over 20-kg, and there is actually a bag weight cost if it is too heavy. After a bit of research, we realised there is actually not a limit on the number of 'checked bags', only on the total weight. So we bought a new four wheel suitcase and distributed the weight between the three 'checked bags' as for parities travelling together it is the net combined weight of all bags that is counted. The 'man bag' from 2013 actually ended up in the bin and I used my backpack in its place, it easily carried my small laptop plus all the other bits and pieces I needed to have access to.
NOTE: We flew Singapore airlines, so check your particular airline bag policy to make sure my comments apply.
I also agree with 'liz.posmyk' about the packing cells. It is far easier to find particular items in the cell rather than looking for them mixed up with other clothes. If you are travelling with others, make sure you have different colours so you do not get mixed up! Also, do not get large cells as they can be too bulky.
A number of web sites about packing for holidays suggest washing underwear in the hotel (motel) sink and hang it overnight to dry. In all our travels my wife and I have never used the hotel sink to wash any clothes. while we have come close to running out of essentials, we always plan ahead and allow for washing clothes either in a laundry or stay at an apartment with washing facilities (can be interesting trying to work an Italian machine in Poland).
When packing do not get to stressed about getting it precisely right, we often get it very wrong. One trip I actually posted clothes home because they were useless and just took up space. On our most recent trip we left Canberra in mid winter wearing heavy clothes and landed in London in mid summer heat, so we had to have a variety of clothes. The warm clothes were particularly useful in north Scotland and Orkneys, but shorts were needed most of the trip.
One last lesson leant at Heathrow Airport as we were waiting to leave. We all know to put lots of identification in 'checked bags' (PS we have, so far. not had any bag go missing). However, no-one mentions putting ID on or in carry on bags. We watched staff going through a left bag trying to identify the owner of the bag, there was not one bit of identification. ( I did wonder why they were going through the bag considering the warnings about not leaving bags unattended, and that they will be taken away and destroyed? )
Sorry if this post is a bit long winded, it might be the jet lag? Hope it helps.