I actually came up with a pretty simple solution. It does involve scripting, but its all done in one place, which should make it easier to deal with. I'll explain it step by step for you (don't feel obligated to use it though, I figured it'd be a fun challenge). So you know, this all goes in the script called GLOBAL PAGE, in the scripts tab (you need scripting enabled).
The code (everything bolded):
%ITEMS := 0
IF $ITEMSTATE1 = 1 THEN
%ITEMS := %ITEMS + 1
IF $ITEMSTATE2 = 1 THEN
%ITEMS := %ITEMS + 1
IF $ITEMSTATE3 = 1 THEN
%ITEMS := %ITEMS + 1
IF $ITEMSTATE4 = 1 THEN
%ITEMS := %ITEMS + 1
IF %ITEMS > 3 THEN
BEGIN
$LINKTEXT1 := ""
$LINKTEXT2 := ""
$LINKTEXT3 := ""
$LINKTEXT4 := ""
$PAGETEXT := $PAGETEXT + "<font color=red>You have too many items. You must drop one to continue.</font>"
END
Okay, so the first thing you need to do is make a variable to hold how many items you have. I called mine ITEMS.
The first block of code, is adding up the number of items you have each time you reach a new page. The basic idea here is each time you pick up an item (which refreshes the page), we will check how many items you have. Since variables carry over between pages, we need to reset it to 0 each time (otherwise it keeps adding +1 for each item, even when you've already accounted for that item). $ITEMSTATE# = 1, is checking if we have that item (if we don't it equals 0, if we do it's 1).
In my game I had 4 items. If you have more (and I'm assuming you do), just copy and paste that part of the code more times, changing the numbers of the $ITEMSTATE## to match your items, until you have all your items covered. You can go to you items tab in your storygame editor to see your list of items and their ID numbers.
The next part is where we actually do the check. In my case, I decided I didn't want the player to ever have more than three items. If they have more than 3, I change the text of the links on the page, to be nothing. No text for the links, makes them unclickable, which means the player can't proceed. I have LINKTEXT1-4 there, because I don't imagine you'll ever have more than 4 links on a page at any given time. If you do, just add more of the LINKTEXT (next one would be fine), until you reached the maximum number of links on any given page.
After the check (assuming it fails the check and they have too many items), I add the line "You have too many items. You must drop one to continue", so that the player knows there is a reason behind why they suddenly can't proceed. The text is also in red.
You should note that this does not prevent the user from actually using any of the items. So they could still use one once they go over their maximum. They can also continue to pick up items after reaching their maximum (but then they'd still be stuck on that page until they dropped enough).
We probably could go into more detail, and prevent them from using any of the items, but that'd require much more effort, and I'm sure most people would comply and drop an item when told to do so anyway.
