True, you can walk in sandals or trainers, but if you want to give the soles of your feet a bit of protection and your ankles some support then a strong pair of lightweight boots are ideal. If your boots fit correctly and you break them and your feet in gently, then you shouldn't get blisters. Boots and feet go together like a good marriage or relationship. Both partners should feel pretty happy at sticking together and should avoid rubbing each other up the wrong way. When it comes to trousers I tend to go for a light pair of cotton slacks in summer and a heavier thicker pair in winter.
Jeans are absolutely hopeless.
They are often too tight to allow leg stretching for those moments when you are leaping barbed wire fences and when they get wet they are worse than useless. Above the waist I usually wear a sweat shirt and a fibre pile jacket when it is cold. The answer to keeping warm really lies in having layers that you can adjust as the temperature changes. As an outer layer I have a Gortex jacket and over-trousers. They are expensive but will last a lifetime.