Ok folks, after reading this thread I think I can offer some clarification. Some of this is obvious to some of you, but others may need the basics so bear with me.
When you are editing your apparel there are set bonuses for each sponsor when you have 5 pieces of apparel all with the same sponsor above level 4. There are common, rare, and epics. (Note commons are much easier to level up, with rares and epics being found in Pro Shop or sponsor packs... usually gold or platinum). Each item has unique characteristics that is independent of the set bonus (slow driver meter speed, iron spin, putting forgiveness, sand power etc). The qualities for each item still work in all H2H matches, regardless of whether you have all the same sponsors or mix and match.
When you activate the sponsor, you get 30 minutes of play to level up your gear. After that time expires, it will reset in 5 and a half hours. During this time when your sponsor is active, I recommend playing Casablanca for 5-7 games to rank up your apparel. Notice in the information section of room, it will tell you a Pack Cap, which tells you what kind of gear you can get. The higher tiers get more points. There are other threads that cover this in more depth.
The set bonuses for the sponsors give you a percentage chance to win the set bonus. Here are the sponsor set bonuses (note the higher your level on all 5 items, say all items level 6 instead of 4, the higher chance of hitting set bonus)
TopGolf 5-15% Chance for 50% refund on a loss
SwingEdge 8-15% Chance to win a bonus sponsor pack on win
MAX 20-45% Chance to trigger a 20% XP boost for 1 hr
Foxwind 15-60% Chance to save a lost ball
C&M 10-35% Chance to get 15% added to C&M stats for 1 hr
HERE IS WHAT YOU CAME FOR... the Wildcard items are designated by the little snowflake icon in the upper left hand corner where the sponsor icon usually is. I got a free shirt for Thanksgiving and Chinese New Year. These items typically do not have any attributes and are for appearance only.
So for example if you really like the Thanksgiving shirt with a Turkey on it, you can keep your other 4 pieces of SwingEdge gear on and still get credit for having all five items to qualify for the set bonus. As long as you have one piece over level 4 equipped, you can use up to 4 wildcards and still qualify for set bonus. So because the wildcards have no attributes, you will look cool, but they do not add anything to your game.
In the pro shop under apparel if you look at the very top menu, you will see things like Puma and UnderArmor. I think these are all wildcard items, but have yet to purchase any of those to find out. WGT sometimes will just send out free wildcard items, usually around holidays.
I hope this clarifies things.
Oh and also, I just figured out I can get around 10 free credits (not coins, credits) a couple times a day just by watching a few videos. Can be found in bottom left corner of home screen. That is enough to get a 3 pack of the 10 credit balls every day, or in a month, save and get a new club without spending any money.