For periodontitis is there any gel or other type of product which can be applied on the gum to stop food entering pockets?

No: Sorry, but even if that were possible, the bacteria, dead cells and plaque would continue to fester and the periodontal pocketing would get worse. You need to have definitive treatment to eliminate the pockets and good home care to prevent their return. Please see a Periodontist for a proper evaluation, counseling and treatment. You need to better understand the nature of Periodontitis.

No: To tighten up the gums you need to get a thorough cleaning and have your pockets evaluated. Healthy pocket depth is 2-3 mm from top of gum to bone level If you have 6mm or greater you need to have the gums reduced back to 2-3 which will prevent further bone loss and healthy tissues.

No : good oral hygiene brushing flossing and rinsing with something like Peridex (chlorhexidine gluconate) will help