To help, you can look up adoption centers near you and adopt stray cats.  It also greatly helps to check your local laws to make sure it's legal to take in and take care of stray cats.  If there are no laws preventing this in your area, you can take in strays and take them to your local vet to make sure they're healthy and not a risk to you or anyone in your household. And even if you don't have the ability to care for a pet, you may know someone who can and wants to.  Word of mouth is a powerful thing, anything you can do helps the cause.

What if I, nor anybody I know, has the ability to take in these strays?

Even if you can't take strays in, feeding them can greatly help extend their survival until someone who has the resources to take them in finds them.  If you regularly see a stray near your house, you can set a bowl of cat food on your porch at around the time the stray cats usually come, though be careful. Cats are a hit or miss when it comes to being able to eat intuitively (in other words, knowing when to stop eating before you make yourself sick.), so don't go overboard with the food.  A small portion should be okay and help the cat to its next meal.  Also, some cats have poor reactions to some foods, so buy from a well-known brand if you do this!