First, do whatever you can to use promos for their intended purpose, within their intended window.
When leftover promotional packs are unavoidable, we recommend using them as extra rewards for new players, returning players from previous weeks, and players who brought a friend for the following set.
If you have left over promotional materials (unrelated to seasonal Promo Packs), you can use them to drive play once the next Standard set releases.
COVID-19: As a temporary change to our general promo policy, you may also use left-over promotional materials as sales incentives for sealed Magic products once the next Standard set releases. If a product has been delayed, you may use the promotional material as intended with the product once the product arrives rather than on its original release date.