Determine whether the acquisition is a desire (a need or just a want), whether it is essential (fundamental or auxiliary) and whether is is suitable (its utility/efficiency) for its intended purpose.
Ask yourself if you already own something that is similar or could serve the same purpose. If not, go on to Test #2
Determine the environmental and social impact of the acquisition. Can you purchase it used instead of new? Ask yourself if it is made locally (saving GHG emissions) by a company who treats its workers fairly, humanely, safely and pays them a living wage. Is the manufacturer fair-trade certified? Is the organization practicing sustainably by using a process that does not pollute the environment, does it use clean energy and does it pay carbon offsets or has a low carbon footprint? Does it follow regulations or has it violated them? Does the company design its product with all of its resources life cycles in mind? (cradle to cradle)
If the service or product you require comes from a company that practices sustainability (not just greenwashing) then can you really afford it? (Cash or barter, not credit)
If your mindful acquisition can pass all 3 tests, acquire it. Otherwise you have saved yourself money and saved the planet.