One possible alternative is if you have a vacuum sealer, is to take an empty quart or gallon bag (these are very sturdy) and seal across the top. When you want to use the bag snip one corner, when filling, fill perhaps ¾ of the way, squeeze out the air and then fold multiple the corner and secure with a paperclip. I have not tried to seal one of the roasting bags, but this might work with those as well, allowing you a more confined bag top. If you have a little extra room in your kit, use a bag sealer clip (you can find these now in most kitchen areas of retail stores. These clips can be used for a variety of applications.
Ikea has a good price 30 clips for $2.99, but other retailers should also have a selection.
Sealing Clips Pete