Your Baggage (it's not what you think)
When preparing to head to an art retreat or workshop, you have a few options available: pack everything but the kitchen sink in your checked suitcase (change of clothing optional) OR shop at your destination or ship to the destination in advance (check with your host prior and clear up any receiving preferences in advance.)
As a venue/organizer/attendee I've seen the gamut of the traveling art supplies, let me help you pack like a pro:
Take your supply list and work from it. Don't put more thought into it than what the list states. The teaching artist has developed the supply list with the class in mind. You don't need to anticipate any unforeseen needs.
Check a bag. No, really. Bite the bullet and check a bag. TSA doesn't take kindly to artists traveling with items above their ever-changing liquid volume maximums.
Check with the current TSA regulations on liquids and flammable items. Do not bring anything onto the plane (same applies to checked baggage) that is either considered flammable or combustible; think cold wax, oil paints, or spray aerosol fixatives, et al. If your supply list requires these things, inquire with the teaching artist or venue, to see if these items are included as part of your registration or if they are available for purchase from the venue.
Don't wait until the last minute to inquire about supplies onsite for purchase - many venues don't sell supplies or only have a limited quantity on hand. If you make arrangements to purchase supplies from the venue or the teaching artist, know what it costs and bring the exact amount (in cash) to the workshop. You don't want to waste time trying to break a $50 bill or have the seller incur credit card fees for your purchase.
Ephemera: unless it's stated that you should bring volumes of ephemera, narrow it down to one or two, gallon-sized, ziploc bags. Yes, I know, you may "need" that perfect piece (or five hundred) of ephemera and guess what, you'll live, you'll adapt, you'll create that kick-a** masterpiece with that specific piece of ephemera when you get home (or not.) Better yet, most people are extremely generous and will gladly share some of their prized ephemera pieces
Ziploc is your friend. Double enclose the majority of your liquid supplies. If you're really worried, encase each medium in a separate ziploc bag and encase it in another ziploc bag. I usually go one step further and put all of my ziploc bagged items inside a clear plastic container with a copy of the supply list right on top for TSA.
Paint: Unless your class requires bringing oil paints or other flammable mediums, you should be fine packing your acrylics. Again, refer to the supply list and ask for clarification if necessary. Remember: Ziploc bags are your friend!
If you are shipping supplies, your package should arrive well before your arrival. Inquire of your host to make sure it's okay and also check to see if your preferred shipping carrier will deliver to the host venue. Not all carriers deliver and you certainly don't want to make your host take on the task of driving to fetch your packages.
If in doubt, allow time when you book your travel to purchase additional supplies at your destination before the workshop.