I use a Linea (House of Fraser) carry on sized case as my workhorse - cost £60 is the sale a few years ago.

I can five days of shirts in it, if I'm doing a conference in the US and packing t-shirts instead I can get a week in it.

If I want to go one bag, I can put my laptop in the outisde pocket (need to find a very slimline messenger to go with it really)

I've used it 45ish weeks of the year for the last two year and it's still in great shape.