How to exclude some files from filename expansion mechanism in bash?

Since you are using bash:

shopt -s extglob
echo rm -rf ./!(bin|sbin|usr|...)

I recommend to add echo at the beginning of the command line when you are running something what potentially can blow up the entire system. Remove it if you are happy with the result.

Note: The above command won't remove hidden files (those which name start by a dot). If you want to remove them as well then activate also dotglob option:

shopt -s dotglob

This command will show all non-directories in /:

find / -maxdepth 1 -type f

Once you have made absolutely sure no files are there that you wish to keep, you can use:

find / -maxdepth 1 -type f -delete

Safer, would be to move them elsewhere to ensure you aren't deleting something you want to preserve:

mkdir /root/preserve
find / -maxdepth 1 -type f -exec mv -- "{}" /root/preserve/\;

If, in addition to files, you also have directories that you've added to the root of the filesystem, this could be automated by excluding the LSB directories from an automated mv or rm, but honestly, since we're dealing with purging things in the root of the filesystem, I would strongly suggest you consider doing it manually if at all feasible.

If this is not feasible, something like this could do the trick:

#!/bin/bash
declare -a excludes
for item in root sys 'lost+found' mnt home proc etc opt boot lib lib64 libx32 sbin media srv dev var usr bin tmp run; do
    excludes+=("$item")
done
if ! [[ -d /root/preserve ]]; then
    mkdir -p /root/preserve
fi
IFS="\n"
for item in find / -type d -maxdepth 1; do
    really=true
    for exclude in ${excludes[@]}; do
        if [[ "$exclude" == "${item#/}" ]]; then
            really=false
        fi
    done
    if [[ "true" == "$really" ]]; then
        mv -- "$item" /root/preserve/
    fi
done

Once you've passed the scream test (i. e. your system still runs and you are not screaming in anguish), you can remove the contents of /root/preserve/.

Important note: Whatever you do, don't even think about running any permutation of rm -fr [ANYTHING GOES HERE] /.

This should get the job done (though not in the same way as the OP asks):

ls -1 >1.txt
pico 1.txt 

remove all files/directories you want to keep

xargs rm < 1.txt

If your files all have the same name format, date, or something else, then there are other methods.

I'd look at the inodes - and see if they are sequential via ls -i |sort and if they are, then the new files will have larger inodes. Then using the same type of process as above...

ls -iF1 | sort |cut -c10- | grep -vE "\/|\@" >i.txt   #This part removes entries that are not regular files, such as directories and links.  
pico i.txt
xargs rm < i.txt

in the cut command above, check your inodes list first to make sure it is the right amount.