Lots of things will work depending on how intense the light you need to block is. If it was me I'd be cautious about using anything that will hold or absorb water so you don't accidentally make a mold factory.

A personal favorite is radiant barrier, found commonly with insulation materials at hardware stores. There are many varieties of it from bubble wrap to foam based but the idea is the same- At least one side is reflective and usually covered in mylar/something highly reflective. It's more expensive to get going but it doesn't break down and is easy to keep clean and reuse. It can also be easily shaped to wrap things like buckets and whatnot.

Another option people commonly use is pieces of extruded foam. NOTE: Not all foam is created equal. Expanded foam is typically frowned on for use in these systems, but it all comes down to personal preference. Not everyone has the same standards for what they feel is ok and I don't personally use expanded foam. It's too pourous and sheds particles far too readily for my liking. Having said that, many of your commercial farms raising plants to be sold in nurseries in the spring are using expanded foam as rooting material, so make of that what you will. When using foam you can even bypass the use of a lid entirely and float your plants in your res if that's something that interests you.

Aluminum tape is another option for low effort light proofing. Most stores will sell huge rolls of it for a reasonable price and it holds up well enough long term. One advantage this has over paint is that it's much easier to take off some tape and replace it if it's damaged or your setup changes instead of trying to strip old paint and start over.

Depending on how intense the light source is something as simple as a space blanket/mylar sheeting can even be used. Most of this material is semi transparent, but it will still block a fair bit of light. Keep in mind if you aren't careful this material can accidentally make your heating problem worse, not better, so I don't like using it outdoors where I can't keep an eye on things.

Not everything needs to have the light blocked.

If you're growing under artificial light and you aren't going to keep the res going more than a month or so between restarts you don't necessarily have to block the light. Greens like lettuce, spinach, etc grow so rapidly that you will likely exhaust the palatable growth before algae or anything else has a chance to start causing you problems. In these cases you can simply wash and disinfect your equipment and start over.