What can I do with a lot of fresh tarragon?
Most fresh herbs can be used to make infusions to use when the herbs are out of season.  You can infuse oil, vinegar, simple syrup or vodka depending on what sort of dishes you typically cook.

You can also make herb sauces (take inspiration from a chimichurri or pesto, but substitute for the herbs you have on hand) or herb butters (mix chopped herbs with softened butter, shape into a log, then chill or freeze).