Feel free to include and edit this language in your supplier contracts to ensure you're able to both collect the data you need and that suppliers will support you in your sustainability efforts.
Sample contract language specifically for providing data:
[THE SUPPLIER/VENUE] agrees to measure data pertaining to energy consumption (including type of energy), waste and recycling, catering and any other as discussed pre-event and to provide the data within a reasonable time after the event (max. 6-8 weeks).
Sample contract language for general sustainability:
[THE ORGANISER] is committed to conducting a sustainable event as is feasible within reasonable constraints. [THE SUPPLIER/VENUE] agrees to work collaboratively with [THE ORGANISER], its appointed sustainability consultants and third-party suppliers for the duration of this contract to make good faith efforts to implement feasible sustainable event practices as requested by [THE ORGANISER]. [THE SUPPLIER/VENUE] agrees to support the commitment internally by engaging and educating relevant departments regarding this commitment. [THE SUPPLIER/VENUE] will communicate to [THE ORGANISER] no later than 90 days before the event executes any barriers to requested sustainable practices that may prevent [THE SUPPLIER/VENUE] from complying.