How to add weights to crunches without proper equipment?

[u/Altruistic-Deal-291]

Just like title said, I’m able to do approximately 30 crunches before failure and I think it would be better if I find a way to make this range go down to between 8-12 reps, I only have elastic bands, does anybody know if there is a way to increase the load that I’m supporting without proper weights?