Will I need to know what to consume one year ahead?
No, you are not expected to know what you want to consume in any detail for the year ahead.
An individual consumption proposal is just a consumer’s best estimate of what they think they will consume in the upcoming year by choosing from a list of broad categories of goods, e.g. “shoes”, “bicycles”, and “computers”. This starts by looking at their previous year’s data, and then adjusting up or down as prices change from round to round during the planning.