Whats the best approach to attaching a saddle bag to a bikes seatpost and clamp, considering the varying diameters and materials used in modern seatposts? Should I opt for a bag with a fixed clamp diameter or one with an adjustable clamp to ensure compatibility with my bikes specific seatpost? Are there any specific considerations I should take into account when choosing a saddle bag, such as the type of clamp material or the bags weight capacity, to ensure a secure and reliable attachment? Additionally, are there any clever tricks or hacks to make the attachment process easier and more efficient, or to prevent the bag from shifting or rotating during rides?