The stomach isn't like a big cave with a pool af acid in it. It is compacted by muscles around it so if you are swallowed whole, you would have to fight against those muscles to even be able to move at all. If your arms are above your head it's likely you would die before you are able to move them to your hips to draw your knives. If they are at your hips, good look moving the knives to point outwards. Also the stomache is lined with thick mucous to protect it from sharp objects...
Also it's completely dark and disorienting.
It's almost certainly you'd drown, suffocate and get crushed VERY quickly after getting swallowed alive.