I don't get what you mean by this, but:
-N64 Memory Card: I assume you mean the thing that plugs into the controller. A lot of portables have this. It's a bit of a pain and it takes up some space but it is easily doable.
-NGC Memory Card: Since you need this to save games, every GCp I've ever seen has this. It's relatively simple to put in.
-NGC GBA Cable: If there are controller ports to plug it into, it'll work. Some portables have all the controller ports, sometimes even P1, some have only P2, some have none, and a new trend is a connector for AV and controllers that connects to a dock. Usually you won't be able to use it as P1 though, not easily. You could integrate the GBA, I suppose.
-GameBoy Player: It'll make the portable bigger, but it could be integrated. As for being able to plug it in, it would be pretty awkward. There was one guy who proposed making a GCp with a Game Boy Player in it, but I don't think it ever happened.
-NGC Lan Cable: I don't know what you mean by this. The broadband adaptor? It could be integrated, or even a slot for it provided on the portable, but why? There is what, one game that uses it? I don't know if there is even service any more. But it's pointless on a portable, because you probably won't have a wired internet connection where you take it anyway.
-Genesis Mega-CD: In theory, you could. In reality, it would be unbelievably big and ugly. You would also have to use the Genesis version 1 or 2 rather than the Genesis 3 or a clone, so that alone adds weight and size. I suppose it would be possible to make the portable able to "dock" with the Sega CD unit, but why bother? There is a unit that would be perfect for this- the Sega CDX. It's a small Genesis/Sega CD combo unit, but it's rare and expensive.
-Genesis 32X: If you did some weird stuff with the AV wiring, provided power and had enough clearance on the cart slot, you could plug it in. It could be integrated as well with some, but not a huge amount of difficulty. There is actually a portable somewhere that's based around a CDX and has a 32X in it as well. Beware of power draw if you do this.
-Genesis Powerbase Converter: I'm not that familiar with this, but I think you could just plug it in if you planned on it. However, it would be huge and ugly. It also doesn't work with the Genesis 3, which most Genesis portables are based on. If you really wanted to, you could probably build a combo unit. You might not even have to sacrifice a Power Base Converter; from what I heard it's mostly just an adaptor with not a lot of electronics.
