Admittedly I still use cat for this.

This also works too, but it’s more verbose:

echo "$(<foo.txt)"

It’s mentioned in the Bash man pages:

The command substitution $(cat file) can be replaced by the equivalent but faster $(< file).

EDIT: I was just informed that simply <foo.txt works too.

cat is misunderstood a lot. The purpose of cat is to combine multiple files together (it’s literally short for “concatenate”), like cat *.log to combine all log files together.

If you’re just using it for a single file, then you should just redirect the file to stdin. These two command lines behave similarly:

cat foo.txt | some-command

some-command < foo.txt

For head, tail, grep and some other commands, you can just pass in the file name directly as an argument (e.g. grep whatever foo.txt).