The current invention may be to provide a modular luggage system having an at least one modular bag that may be configured to be secured to a cart configured to be fully-collapsible. In this embodiment, the collapsible adjustable cart may be configured in a nested configuration such that it may be a unibody structure that may be easily collapsed and stored, preferably in one or more modular bags. In this embodiment, the cart may further include a plurality of telescoping arms coupled to a base support as well as a plurality of extendable wheels secured to the base support through at least one wheel coupler. The adjustable support surface may be expandable through the use of one or more collapsible surfaces such that it may better accommodate one or more modular bags. The invention may also provide a belt-mounted stair guide mechanism to assist a user maneuver an adjustable cart up stairs, or other irregular elevated surfaces.