Nine things to put in your rucksack
1. Map and compass
Unless you're really sure you know the area. If you get lost, have an emergency or just decide to change your route, the 1:25000 Explorer map will show you all sorts of useful things such as roads and paths, the nearest village or buildings. The batteries or signal won't fail.
2. Lipsil / Chapstick
I hate getting sore lips, and when you're walking you're more prone to getting dehydrated which leads to this problem.
The runny nose can strike when you're walking, especially in winter. Plus a variety of other uses.
4. Sun Block
Many hours in the sun, or even under cloud if it's summer, can burn your skin. Besides being unsightly and a bit painful, such exposure to the sun can put you at risk of skin cancer. Keep a tube of total sun block or high SPF in your rucksack and you won't be caught out.
You'll get through more water than you think. A litre per person isn't too much if you're out for several hours, and twice that if it's hot. On very long walks on very hot days, I've found even a gallon isn't enough. That's a lot to carry, so perhaps plan to buy some on the way, but carry enough so that you don't run out - dehydration isn't fun.
6. Cake / Fruit
It's surprising how many calories you burn when walking. It sounds great if you're trying to lose weight but if you don't eat plenty while walking, you'll be flagging. At 300 - 400 calories burned per hour (depending on your weight and walking speed) on a good day's waking you can eat 2,000 calories while walking, on top of what you'd normally eat that day, and still be in deficit.
Chocolate is great for a fast boost, but don't forget the carbohydrates for slower-release energy. Cake such as fruit cake or malt loaf tastes great as well as packing the calories into a small space.
You'll see many wonderful things while walking, you'll kick yourself if you forget a camera, (bonus if you have a good one on your phone).
You may not see the need to carry the weight if you know you're going to finish before it gets dark. But many walks take longer than planned. It's not fun being in the middle of the countryside after dark, trying to read the map by the light of the camera's LCD screen and then trying to find the gap in a hedge!
A small wind-up one kept at the bottom of your rucksack is a great idea. The batteries won't be flat and won't go flat.
It's easy to forget. You may be wearing different trousers and jacket when you're walking than you normally wear during the day. But it may be essential for food / water, an emergency taxi, or just a well-earned pint! Keep a note tucked somewhere in your rucksack to be sure of always having some handy.