Interesting products to seal up firewall "holes"

[ModernMuseum]

Do you guys have any interesting products that you've used to close up holes in the firewall, such as

Slot where a a hydraulic clutch rod might go through
Cluster of electrical cables passing through?

I've got a ton of sound deadening in the car, but I think there's quite a bit of noise coming through these types of holes.

[Mr Nick]

Blank grommets https://www.holley.com/products/plumbing_an_fittings_and_hose/seals/grommets/

[79 Camaro]

When I need grommets I go salvage yard diving. There are all shapes and sizes on late model cars. The yards don't charge hardly any thing for them.

[CarlC]

If looking to plug small holes these kits work pretty well. https://www.aliexpress.us/item/3256801314441613.html?spm=a2g0o.productlist.0.0.16 724068osWJXB&algo_pvid=b5dd86b9-e0e9-42c5-9966-ae15fda2b97a&algo_exp_id=b5dd86b9-e0e9-42c5-9966-ae15fda2b97a-5&pdp_ext_f=%7B%22sku_id%22%3A%2212000016362351875%2 2%7D&pdp_npi=2%40dis%21USD%218.96%214.48%21%21%21%21%21 %402101d64d16652060280541100e5653%2112000016362351 875%21sea&curPageLogUid=oZdeXDe5WpSr