You are the best friend that anyone could have.

[yi-ing]

What are the differences between these sentences?

You are the best friend that anyone could have.
You are the best friend that anyone can have.

I can't have you tied to me! I don't want you to miss all the things that someone else could give you.
I can't have you tied to me! I don't want you to miss all the things that someone else can give you.

 

[Raymott]

Sentence 2 makes no sense. Not just anyone can have that person as a friend. As a hypothetical case, they could.

The second example is similar. You're making an assumption. It also requires 'could'. You don't know that there is someone out there who can give this person all those things.

 

[yi-ing]

The problem is that why we can use "can" in the following sentence but not in the examples above?

Parents can save money by booking their holiday outside the peak season.
These 12 foods are filling relative to their calorie content, so you can eat a lot of them without getting fat.

 

[Raymott]

1. In the first sentence, they literally can save money by doing this. You can't answer that with "Well, maybe they can't" which applies to the previous sentences. In reality, they or you or anyone can (all other things being normal) save money by holidaying in the off-season.

2. Here, 'can' either means 'may', or the same applies as above.

In both of these sentences 'could' could be used depending on your meaning.
A: "You can eat these foods without getting fat."
B: "But I want to get fat."
A: "OK, I'm just saying you could eat them without getting fat if that's what you wanted."