Security, efficient packing and protecting the contents of your bags from the elements should be considered when preparing for travel. Padlock all your zips together and take a chain and lock system such as the Cable Lock to secure your bag to a fixed point on long journeys; bus roof, railway handrail etc. where you may be distracted or lose sight of it.
Use packing cubes and dry bags to organise your clothes and accessories - they will also protect your contents from damp, sand and rain. Backpack raincovers are great in areas where rain can hit hard with little warning; they are super light weight and pack down tiny but can be whipped out in seconds to protect everything in your bag from downpours. Luggage tags will help you identify your bags at airports and will help them find you should the worst happen and your bags go missing.