In the UK, I usually wear some polyester/cotton no-name hiking pants. The ones I use have a fairly narrow cut so they are not too flappy and also have non-bellowed cargo pockets. I secure them with metal trouser clips.
Temp range is 0-24C, dry -damp. If it rains I add some waterproof over-pants or they dry out in 20 mins.
Above 24C I often wear shorts.
My current job is pretty casual dress so I commute, work and relax in the same clothes.