I play in Adventurers League and have a character that has a +1 Ring of Protection, which gives +1 to AC and saves. I also have a Stone of Good Luck which gives a +1 to saves and ability checks.
If I equip both items and my base Dex save is +4, would it become +6 due to receiving both bonuses, or +5 with just one? I can't find much in the PHB or Google to answer this.
Yes. In general, bonuses stack1 ... J. Crawford, Sage Advice
See the Caveat below for making sure that you discuss this with your DM before the session begins.
They are two different magical effects from two different items. There is no text in either description that indicates that they would not stack. What would not stack is two RoP +1.
DMG p. 138
A creature can't attune to more than one copy of an item. For example, a creature can't attune to more than one ring of protection at a time.
The stone of good luck helps with ability checks and saving throws, while the Ring of Protection helps with AC and saving throws. They are not identical items. As long as you have no more than three items attuned, and these two are among them, the rules do not preclude them stacking.
Combining magical effects is covered in the PHB (p. 205). Since each item is different, though they both provide beneficial effects, they should both continue to work.
From the Sage Advice compendium. (This is posted on the WoTC site. Unless the AL expressly rejects Sage Advice, it should cover your situation. (Page 16, Sage Advice, Version 1.14, @2016 Wizards of the Coast LLC.)
Do the AC bonuses from a ring of protection and bracers of defense stack?
Yes. In general, bonuses stack, unless they’re from the same spell (see “Combining Magical Effects” in the Player’s Handbook, p. 205). You also can’t benefit from more than one ring of protection, for instance, since you can’t attune to more than one copy of an item at a time.
Whether or not any given Dungeon Master chooses to utilize Sage Advice as a resource for rules adjudication in D&D Adventurers League play is at the discretion of each individual DM. (A.L. FAQ) (Credit to @Miniman for catching this).
As you say, there are no rules against stacking the bonuses of magic items. Indeed, effects that could be stacked in previous editions are now carefully worded to prevent stacking (such as Mage Armor).
Stacking problems are balanced by the attunement requirement (DMG 138-9). Both the Ring of Protection and the Stone of Good Luck require attunement, and you can only attune to 3 items at a time. This means that you're spending 2 of your 3 magic item slots to get your +2 bonus. Depending on your level and your DM, this might be worthwhile, or it might be a waste of attunement slots.
Additionally, note that the DMG explicitly forbids attuning to two copies of the same magic item, so you can't attune to two Stones of Good Luck to double your bonus.
