I use tung oil for lots of stuff, and it is a really good sealer in and of itself. I use several thin coats, letting it dry well in between each coat, and on the final coats I use some 0000 steel wool to buff the finish a little before the next. You can get a glossy glassy finish that way, and it seems to be water repellent after it drys. Does take a while to dry though, especially in high humidity (central alabama). I don't think shellac would help it, and if shellac is on there first you don't get the penetrating benefits of the tung oil - I don't know if it would peel but it would not help the wood any which is why I use it.
You can buy food safe tung oil that you can use on wooden bowls and utensils too.