Everybody has their own preferences on what to carry for a day’s walking, depending on experience, activity, season and terrain, but there are some items that everybody should carry in their rucksack when walking in Autumnal weather:
Spare Clothing - It might be mild when you start off, but Autumnal weather is notoriously unpredictable. Climbing out of a valley can expose you to higher wind speeds and higher elevations can cause temperatures to plummet. Ensure you have extra warm clothing with you such as an extra base layer or a lightweight down jacket.
Thermal Hat & Gloves - Temperatures can drop very quickly when the sun starts to set. Ensuring you have a warm hat and pair of gloves to hand will help you keep warm.
Drink - Dehydration can happen in any weather conditions, so ensure you have access to water or even a flask of hot tea/coffee. Drinking little and often will help stave off thirst, which is a sign of inadequate liquid intake.
Food - If you are planning to walk all day then you will need to pack a good lunch and have snacks available to boost blood sugar levels if you start to fade. It's good practice to stash a high energy treat, such as a chocolate bar, in your pack for emergency use only.
First Aid Kit - You will more than likely complete your walk without incidence. However this is not guaranteed, so you should pack a small first aid kit that will enable treatment of the most common injuries sustained when walking. If you need any medication, then make sure you carry at least two days supply with you.
Lighting - With daylight shortening, getting caught out in poor visibility is a real possibility. Carrying a small torch or head lamp is essential... and check the batteries before you set off!
Shelter - You don't need to carry a one man tent, but having the ability to shelter from worsening weather conditions is a must. A simple plastic survival bag can be deployed in emergencies to offer protection from the wind and rain.
Navigation - If your intended walk is new to you, then ensure you familiarise yourself with the directions in advance, and always have an escape route so you can cut the walk short should the weather take a turn for the worse. Carrying a map or a digital route planner is always a good idea.