Metal tins are 'classic' containers by virtue of availablilty. Tobacco and candy tins are the usual resource. Few will be even remotely waterproof. A simple expedient is to secure the box with tape. This happily provides a redundant resource for repairs. Don't be afraid to 'think outside the box.' Round tins such as saddlesoap containers often have a threading vs hinge assembly. Round materials such as snarewire and pocket saws become easier to stow vs angular items in square units. Packing a PSK is an almost religous experience or right of passage anyway. Another overlooked step is to give a quick wipe down of the contents. Salty fingerprints have a nasty habit of initiating rust. To get started just pick up a tin of ALTOIDS. Think of this as your prototype. Eventually you will be ogling everything from aluminum cigar tubes to EBAY sterling silver snuff boxes.