The starting point for this could be a simple loop:

while IFS= read -r item
do
    [ -f "$item" ] && printf '%s\n' "$item"
done <file.txt

This could be crashed onto a single line at the expense of readability:

while IFS= read -r item; do [ -f "$item" ] && printf '%s\n' "$item"; done <file.txt

Or you could use Perl:

perl -ne 'chomp ($item = $_); print if -f $item' file.txt

The starting point for this could be a simple loop:

while IFS= read -r item
do
    [ -f "$item" ] && printf '%s\n' "$item"
done <file.txt

This could be crashed onto a single line at the expense of readability:

while IFS= read -r item; do [ -f "$item" ] && printf '%s\n' "$item"; done <file.txt

Or you could use Perl:

perl -lne 'print if -f' file.txt