The name of the game for packing gear for hiking is layering and having the right fabrics. Bringing many layers of clothing for a hike – for example a technical shirt, thin top, thick fleece, down jacket and rain jacket – allows you to stay comfortable no matter what you are doing. You can vary the amount of thermal insulation you have, the breathability, and the waterproofness of your clothing on the fly. Cotton clothing can become dangerous in the wilderness. When jeans and cotton hoodies get wet they stop insulating you, and actually suck the heat from your body.
To pack all your gear you will require a solid 25-50 Litre day pack. When buying a daypack make sure it has good suspension so that the weight of your gear will be centred on your hips.
Additionally, consider how long the hikes you are doing and the gear you have. Remember that if you are doing level four or five hikes that you should be bringing a first aid kit, extra food and water, and an emergency sleeping bag or extra clothing. Also consider the features you might want – many pockets, compression straps, hydration sack compatible, etc.
Mountain weather can change suddenly. It can be pristine and sunny one minute and then pissing rain the next. Always bring rain gear and warm clothing as you never know what the afternoon will bring. It’s better it being sunny and your down jacket remaining in your pack then freezing your buns off and having to leave a vista early.