I need to make a savory snack to take on a weekend retreat. Make Thurs/Fri, good through Sunday. HELP! Something fabulous.

I would make spiced nuts. They're filling and gluten-free, and go well with cocktails or regular drinks. If there's a microwave at your retreat, it's nice to warm these up, but not essential. http://whiskandcleaver.com/bar-nuts-ill-take-mine-sweet-spicy/

I've never frozen the spinach bars (seriously we end up eating them for breakfast, lunch, snack, dinner), but I did a quick look and it appears they can be. Reheat in a 350F oven for 15 minutes or until hot. Good luck! The parm shortbread looks really nice as well.

I love the cheese straws from Smitten Kitchen. One recipe makes more than you'd think!

http://smittenkitchen.com/blog/2009/06/cheese-straws/

Will you be able to store the snack in a fridge overnight? If so, these two Turkish dips from Ana Sortun (chef of Oleana in Cambridge) are unusual and delicious, and either would be great served with crudités, bread, and/or pita chips:

hot pepper labne (a yogurt-like dip with pickled green hot peppers mixed in:
http://www.findeatdrink.com/Index/Etc/Entries/2010/9/20_recipe_hot_pepper_labne.html

muhammra (a red pepper-walnut spread):
http://muchdependsondinner.blogspot.com/2009/06/muhammara.html

I'd go with on of the mentioned snack mixes and some homemade beef jerkey.
Make twice as much jerky as you think you'll need.
This is a good recipe. https://food52.com/recipes/22529-bulgogi-jerky
I add a bit of sirachia sauce to mine.

What about grissini/breadsticks? Could be flavoured with Parmesan, sesame seeds, poppy seeds, anchovy, pesto...

Oatmeal cookies, recipe on top of Quaker Oats tube. Use butter. Sub choc chips for raisins. Bump up cinnamon. The salt in them makes them both sweet and savory. They get better by the day.

Other people will be bringing things as well, and that there will be "real food" provided? I would suggest Nicholas Day's savory granola - it great just for munching on, but can also be added to other things (salad, yogurt, veggies, whatever) for some added crunch and flavor

https://food52.com/blog/10530-walnut-rosemary-savory-granola

I'd make a whole bunch of snack mix. I think there's an article here on making snack mix without a recipe, but here's mine: https://food52.com/recipes/8370-sweet-and-spicy-pretzel-and-nut-mix

Try these simple, delicious and even a bit healthy spinach bars http://2aprons.wordpress.com/2014/09/25/spinach-bars/

Dorie Greenspan's cheese crackers (I think she calls them cheez-it-ish crackers) are really tasty and last for several days. You could also make savory biscotti (brown butter and sage, pepper and Parmesan, or mustard and cheddar would be nice combinations).

I'd recommend parmesan shortbread - Nigella Lawson has a fantastic recipe in nigellissima. It's very easy to make, and even easier to transport. Most importantly, they're amazingly delicious, as long as you use fresh parmesan.