Atomically-thin two-dimensional (2D) materials including graphene and transition metal dichalcogenide (TMD) atomic layers (e.g. Molybdenum disulfide, MoS2) are attractive materials for optoelectronic and plasmonic applications and devices due to their exceptional flexural strength led by atomic thickness, broadband optical absorption, and high carrier mobility. Here, we show that crumple nanostructuring of 2D materials allows the enhancement of the outstanding material properties and furthermore enables new, multi-functionalities in mechanical, optoelectronic and plasmonic properties of atomically-thin 2D materials. Crumple nanostructuring of atomically thin materials, graphene and MoS2 atomic layers are used to achieve flexible/stretchable, strain-tunable photodetector devices and plasmonic metamaterials with mechanical reconfigurability. Crumpling of graphene enhances optical absorption by more than an order of magnitude (~12.5 times), enabling enhancement of photoresponsivity by 370% to flat graphene photodetectors and ultrahigh stretchability up to 200%. Furthermore, we present a novel approach to achieve mechanically reconfigurable, strong plasmonic resonances based on crumple-nanostructured graphene. Mechanical reconfiguration of crumple nanostructured graphene allows wide-range tunability of plasmonic resonances from mid- to near-infrared wavelengths. The mechanical reconfigurability can be combined with conventional electrostatic tuning. Our approach of crumple nanostructuring has potential to be applicable for other various 2D materials to achieve strain engineering and mechanical tunability of materials properties. The new functionalities in mechanical, optoelectronic, plasmonic properties created by crumple nanostructuring have potential for emerging flexible electronics and optoelectronics as well as for biosensing technologies and applications.