Just to build on what @Swamidass has said, and include my career experiences on the technical side of the biological sciences. I have actually trained a fair number of undergrads in lab focused summer programs or internships, so I have a little bit of experience seeing potential gaps between education and application.
There are many skills that are needed, but there is one skill that is absolutely required in the sciences, and that is confidence in basic math. If you can’t do something as simple as calculate the molarity of a solution or back calculate dilution factors, then you just won’t be able to make it in the sciences. I have seen at least two students who couldn’t do the basic math, and it prevented them from getting anything valuable from their internships. You also need to the ability to learn more advanced math, like statistics or non-linear regressions. I really think that ability comes from gaining confidence through good study habits and isn’t something innate or something you are gifted with. One way that I think homeschool students could get a firmer grasp on basic math is to learn how to use Excel to analyze data sets and make graphs. This skill set is very useful in the sciences, and I think it helps students to get a firmer grasp on the theory of applied math instead of focusing just on specific problems.
Communication skills are also extremely important, and I think one ways of improving those skills is to teach others. In my own work I have to present data and analyses to the PhD’s I work for. I have to help them understand the methods I used, the basic concepts of lab techniques, why I chose those methods, and properly communicate what conclusions the data points to and why. I know the data, methods, and concepts inside and out, but the hard part is getting other people to understand them. That is where communication skills come in. In a homeschool setting I would consider having students learn a topic and then try to present that material to people who may not understand that material. After a lot of practice you learn how to boil a topic down to what is important, and how to clearly present those ideas. Learning PowerPoint is also a great skill to have, and something homeschoolers could have a blast doing. Standing in front of an audience also gives students confidence that they can later call upon in their professional careers.
The last skill I would include is critical analysis. What does a graph say, and why? What is missing from a certain study? One of the skills that good scientists have is the ability to understand what the data is saying and what the data can’t say. To use a really simple example . . . 100 people with headaches took Drug X and 30% of those headaches went away. What can you say from that data? Actually, not much. How many headaches would go away without taking any drugs? Does taking a pill produce a psychosomatic reaction which alleviates the headache (i.e. placebo effect)? This type of skill set is vitally important in science as well as many other trades such as car repair or engineering.
I would say that 95% of the things I needed to know in my current job in the biological sciences I had to learn on the job. You have to learn how to learn, and gain the confidence needed to tackle problems that you currently don’t understand. I have seen students who freeze up when faced with failure, and I have always found that to be rather frustrating since a large part of science is failing at something over and over until you succeed. As Edison said, he learned 1,000 ways not to make a light bulb. It isn’t about succeeding right away, but being confident in your knowledge once you get there.
Anyway, those are my observations from my 20 years of experience in the sciences, albeit outside of academics. I hope they can be of some help.