You should play around with different amounts of sugar at different times in practice. If you're hypoglycemic (potentially), you'll want to know how fast you're metabolizing sugar. This is pretty easy to figure out. Make sure your coach knows you're doing this. Between you and your coach, if you eat a specific quantity of sugar immediately at the start of work out (literally, right before you dive in), you should be able to pinpoint when it hits you and when you crash. Try it a couple times and in different types of work outs... just get to know your body and how to time it.
As for the start of practice and feeling a bit sick if you eat too soon, I found powerbars to be really helpful. I was a distance swimmer, so the protein and more complex carbs were more helpful, but it was a lot of energy that didn't take up a lot of stomach space.
If I wasn't taking a few bites of power bar, I would usually have two waterbottles: one with water and one with some powdered drink mix (I used "e-load"). I'd use the water only one for the first part of practice and then the e-load one for the latter half. Ultimately, you want to be able to have some sugar right after practice so you can use it to recover, so don't take too much before then.
Another thing to look it might not necessarily be sugar, but monitor your intake of more complex carbs during the day (and supper for the night before). Whole wheat is generally better and slower to metabolize, making for much less volatile blood sugar.