An adjustable reusable modular packaging crate and assembly kit is purposed for safe transportation of preferably mostly two-dimensional items. Several latching corner subassemblies each hold two perpendicular frame extensions that may be locked into adjustable lengths to make crate frame sides. Sets of adjustable clamps interact with the item to be shipped and the crate frame, to assist in securing the item to be shipped. Extendable frame components allow for a frame that adjusts precisely to the size of the item to be shipped. Frame locks securely fix the dimensions of the packaging crate. Gusset subassemblies and cross-corner struts add rigidity to the crate. Corner, frame, strut, and gusset components interlock to create a rigid packaging crate. Frame links enable crate frame sides to be connected side-by-side, adding to the depth of the crate frame. The modular crate may be easily disassembled for low-space storage between uses, and easily reassembled for reuse.