While supplies from earth will be needed to get a colony started, that is not economically viable for most things. Colonist must become self sufficient ASAP. This can happen quickly and with the least amount of colonists if we focus on a limited number of things they can be trained for and get experience producing from local resources. Adaption of the Global Village Construction Set to the mars setting gives us a good place to start.
Humans need certain things to survive. A habitat provides protection from the environment (even on earth that can kill you.) We need food, water and air to breath. We need energy. ...and other things like sewage disposal (have an RVer explain a honey bucket to ya.)
An industrial ecology are those things related in a way that they can create themselves as well as all other things. Keeping these things to a limited number helps us determine the least number of colonists required to have theoretical self sufficiency. Actual self sufficiency will require somewhat more to have the labor force required, but it shouldn't be that many more. As few as perhaps a few dozen items can be the starter kit that provides full life support for all colonists.
We start with martian soil and atmosphere for raw materials. Compressed soil can provide a building material. Power can be in the form of electricity or hydraulics. Combustion engines can produce either. Solar power can be used either directly or to produce fuel for engines. Sunlight can provide the energy for food production. They will need to produce plastics to construct those farms.
Getting to mars will require high technology, but actually living on mars does not. One of the most important things they will need is cheap energy. Without lawyers nuclear energy on mars could be magnitudes cheaper than here on earth.
A future article will put together a mars starter kit listing a minimum of essential items for a complete industrial ecology. Update: ok, it didn't end up being a list of interrelated items. I'll have to continue to work on that.