Bags of holding come in four types and each is given a cubic measurement and a weight for what it can hold. But what can one actually shove into a Bag of Holding?
Could a tower shield?
Some will argue that only something you can put into a large sack shaped container can fit through the opening of the BoH.
Others that the BoH is magic and will "unhinge its jaw" like a snake to allow virtually anything in.
But what is the generally accepted interpretation, and what is official?
Generally, I allow a BoH to hold anything reasonable as long as the dimensions of the object and weight are taken into consideration - since a tower shield is almost the size of a fully grown adult humanoid, it would fit into the bigger bags easier. (I generally assume since each successive 'BoH' is heavier than the last and holds more than the previous one its generally bigger and can hold bigger objects through a bigger opening).
As long as you take volume/space and weight of an object into consideration, theres no reason any piece of equipment a character can carry cant fit into a bag - after all, where else are you going to store such a heavy thing?
The 'Handy Haversack' on the other hand like the 'BoH' works in a similar manner but it specifically limits objects to several much smaller extradimensonal spaces but with the extra benefit of being able to instantly find what you need in any 'pocket' on it automatically.
So yes, a Tower Shield in my opinion could fit in a BoH, its perfectly reasonable to assume - just nothing too ridiculous...trust me, as a GM I have heard my players try to 'Steal' large heavy things by opening the bag over something and pulling it down over statues and so on - but the weight and size limit usually fill the bags fast in those cases.
AND...some players even carry their comrades in them (though you do have to worry about limited air supply and a character outside the bag has to 'reach in' to grab them one at the time and pull them out into the world). Just to help the party 'sneak' around on the Party Rogues personage, but you need a decent 'BoH' to hold several people...lol, plus one of these times that Rogue is going to get caught BEFORE he can retrieve his friends...it'll be fun when that happens.
AND...some players even carry their comrades in them (though you do have to worry about limited air supply and a character outside the bag has to 'reach in' to grab them one at the time and pull them out into the world). Just to help the party 'sneak' around on the Party Rogues personage, but you need a decent 'BoH' to hold several people...lol, plus one of these times that Rogue is going to get caught BEFORE he can retrieve his friends...it'll be fun when that happens.
For this I would recommend the portable hole!
That you could...lol, but make sure to keep other 'Extradimensional Spaces' away from one another, putting say - an 'open' BoH into a Portable Hole still causes a planar rift into the Astral Plane I believe if its the same as 3.5...lol, I havent read up on it yet in Pathfinder but I am sure it works the same way. Not an ideal way to 'get away' from enemies (plus it spews the contents of both across the Astral Plane forevermore...lol).