In the youtube-video [How to Seal Plastic Bag at Home #Ludvic #Maker](https://www.youtube.com/watch?v=wy6teIQI6aM), demonstrates a rather hackish way of sealing plastic bags. In essence what he does is lay the plastic bag flat, put a piece of paper over the top of the bag and then use a soldering iron to transfer heat through the paper and melt close the plastic bag.

Variation over this method could be to use other heat sources:

* soldering iron (as suggested in video)
* edge of clothes iron
* hot glue gun (possibly without glue?) (that is use the heated tip of the glue gun, not the actual gluing capabilities :-) )
* some other heated metal-strip

The point of using the paper between the bag and the heat source, I contemplate is to avoid getting melted plastic on your heat source. 

I would also consider double sealing them for additional strength. That is don't run the sealing strip only once, but twice across the top of the bag.