A strategy to increase the biobased content and use of side-streams in plastic materials is to mix in biobased fillers available as inexpensive by-products. In line with this, herein, results on a polyolefin polymer with added wood powder (with or without a thermal treatment) and oat husk are presented, to make vacuum-formed products. The composite material is compounded, with or without a coupling agent, and then compression molded into sheets that are subsequently vacuum-formed. Despite a large content of fillers, the surface finish is in general smooth and uniform. The presence of filler increased, in general, the stiffness, and the use of the coupling agent is beneficial for the mechanical properties. The ductility and toughness, decreased in the presence of fillers, but the strain at break remained always larger than 10%. The fillers are all more hygroscopic than the polyolefin, which led to an increase in water uptake in the composites when immersed in water. The largest uptake, but still below 3.5% after 5 weeks, is observed for the material with oat husk. The results are overall promising, and open up for the use of biocomposites derived from industrial side-stream biofillers in vacuum-formed products.