Assuming that you have the right kind of a backpack according to your requirements.
First, you need to separate things that you need frequently and things you'll need less often. The way I camp/trek and plan things, I am okay to pack everything all over again in the morning.
Generally, it is best suited to pack lighter items in the bottom of the pack and heavier stuff toward the top, the idea is to keep heavier stuff closer to your back and not on bum. This keeps your center of gravity relatively high. Center of gravity plays a very important role in balancing your body when in motion. Higher Center of gravity tends to make it easy to haul the backpack easily while your performance with balance is hampered. Women naturally have a lower center of gravity, so the women I know and trek with, they pack heavier stuff at the bottom, that further increases their stability.
Remember, The lower your center of gravity is , the easier it is to keep yourself balanced, pack feels heavier. The higher your center of gravity is, the easier it is to haul the pack but chances are more to dwell/tip off or go off-balance.
- If your pack doesn't have a separate space for sleeping bag, keep it at the bottom, usually you'll only need it after you are done for the day. So extra Clothing and your sleeping bag can go lower sections of the backpack.
- Heavier items like water bottles, tins, food and fuel up against the pack’s back panel, and not in the front. If you place the heavy items on the outer sections of the backpack, you will experience that the pack constantly putting you off-balance, leaning back.
- Importantly, keep the Headlamp, Flashlight, Medical Kit (Um, wait, you do carry these, right?) always handy, i.e. upper most sections of the pack.
- Unimportant things like Jellys, Bars you can keep in the top outer section of the pack.
- A well-folded Garbage pack can find its place in the side-pouches if there are any.
So, order of packing:
- Sleeping bag
- Extra Clothes
- Food (Heavy meal)
- eat-on-the-go Food for next day (Lighter)
- Liquid items (Water, juices, fuel bottles/can)
- Hydration pack (closer to the back)
- eat-on-the-go food for today (Lighter)
- Electronic equipment like portable chargers, camera lenses
- Medical Kit, Headlamp, Flashlight.
- Rain Cover