Most often, agent-based situated simulations use reactive agents. While the use of this paradigm offers a rather natural way to build simple behaviours, it is not so easy to define complex behaviours, and these are often built ad hoc and requires precise adjustements. Moreover reactive model is not well fitted to describe deliberate group behaviours since it is more intended to emergence. For these reasons and in order to obtain more explicative models, we are working on proactive agent-based situated simulations. We aim at proposing a generic cognitive agent model. Such agents must build plan to achieve some goals and thus to propose a behaviour. In this paper we show why and how classical planning works must be adapted to the particular context of spatially situated agents in simulations.