One of the most prominent recent efforts was the line-item veto, but the Supreme Court (rightly) said that it requires a constitutional amendment.
You also have to be careful what you wish for. For years everybody bemoaned so-called earmarking. Congress finally prohibited earmarking in their procedures. But many academics have suggested that an unintended consequence was less compromise and greater partisanship in Congress. See https://en.wikipedia.org/wiki/Earmark_(politics) At the end of the day lawmaking and especially budgeting is fundamentally an ugly business. We should be careful about being overly cynical or fatalistic about it. The most important thing is transparency, but that requires the electorate to be more practically minded and less idealistic.
Line-item veto sounds interesting, but extremely dangerous. Some bills meanings and intent could be completely reversed by vetoing a single provision in e.g. definitions section. This wouldn't fix the bundling issue, it would just make the president another party in it, and give them super-congressman powers with the ability to essentially make legislature all by themselves. (And the first couple of paragraphs on the wikipedia article [1] confirm this.)
You're right about being careful what you wish for. That's half of the reason why I didn't try to present a solution: the problem is conceptually clear, but any specific solution will be muddied by the complexities of reality.
Here's my idea anyway: an independent legislative committee whose purpose is to find bundling in bills and can split/veto/force a rewrite before it can be voted on. A supermajority vote can override it. While we're at it, lets also task it with creating an official name that describes the bill without "cutsie" nicknames that misrepresent the content. But as with most "do it with a committee" solutions, this just pushes the problem down a level. We still need solid definitions for things like "bundled" and "related" and "representative" and a way to evaluate the effectiveness of the committee and to challenge their decisions (supreme court? ugh). So I guess this is less a solution and more just a different way to describe the problem.
Feel free to tear the above apart, but that's kind of the point. I'm glad I'm not the one making laws.
> Line-item veto sounds interesting, but extremely dangerous. Some bills meanings and intent could be completely reversed by vetoing a single provision in e.g. definitions section.
Line-item veto, both where currently used in states (for the most part, Wisconsin seems to be a radical exception) and when it was (unconstitutionally) adopted at the federal level, does not allow that.
It allows separate veto of individual appropriations of money within a bill that included one or more appropriations. It doesn't allow separate veto of arbitrary provisions of law.
This can still drastically alter the intent of a bill, but not it in the way you suggest.
There's a difference between allowing a line-item veto (which is a very bad, dangerous thing) and something which prevents unrelated legislation from being packaged together.
You also have to be careful what you wish for. For years everybody bemoaned so-called earmarking. Congress finally prohibited earmarking in their procedures. But many academics have suggested that an unintended consequence was less compromise and greater partisanship in Congress. See https://en.wikipedia.org/wiki/Earmark_(politics) At the end of the day lawmaking and especially budgeting is fundamentally an ugly business. We should be careful about being overly cynical or fatalistic about it. The most important thing is transparency, but that requires the electorate to be more practically minded and less idealistic.