My front crown has come loose and falls off easily. Can a put superglue or equivalent on post and stick it back in the hole?

You could glue your crown back on with denture adhesive until you are able to see a dentist, but I would not use anything permanent, because this may cause damage to the crown or the prepped tooth underneath the crown, once it is removed, cleaned and affixed by your dentist.  The absolute best option would be going to a dentist, ASAP, before your prepped tooth accumulates decay or the crown is damaged.  A simple reattachment of a dislodged crown at a dental office is only about 50 bucks or so.  If you wait and the prep gets decay on it, then you're looking at about $1200-$1500 for a new crown and prep.  Good luck and I hope this helps. Follow me if you have more questions.Sarah Thompson, DMDReal Self 100

If I'm reading your question correctly it sounds like you're looking to find out what you can use to repair the crown but please don't try to do this yourself. A qualified dentist is best-suited to repair a crown for you with the right adhesive. It's not a good idea to attempt this repair yourself. 

It's never a good idea to use superglue because it is hard to control and it can stick things together that you don't want(such as your lips) and it probably toxic in the mouth. This is definitely a job for a dentist. the crown came loose for a reason. If all fits well, perhaps it can be recemented, but more than likely, the root of tooth has cracked or the tooth has broken off inside the crown. This needs attention to take care of it properly and to prevent further damage.