These crates contain non-hazadous goods as denoted by their colour. Non-Hazadous Goods are any products that do not pose a risk to the life or to local flora and fauna, the contents could be clothing, tools, toys or non-hazadous construction materials.  It is not uncommon however for unscrupulous individuals to smuggle goods in non-hazadous cargo boxes, especially on short trips and leaving them at dead drops.