Inventory, Exploration, and Resting

Before digging into more talents, let's recap and expand upon some basic mechanics of the little ruleset I'm putting together by clarifying two central ideas: inventory and the encounter die.

At present, all PCs start with fourteen inventory slots. Additional slots are awarded if their strength, constitution, or intelligence scores exceed 15. This can happen three times as a result. If all three of these scores are above 18 (which takes a while to accrue in any campaign), they're awarded with another bonus trio of slots. That is to say that any PC will only ever have between fourteen and twenty slots. No less, no more (well, unless some wonky magic item or godling's blessing shows up, of course). In this framework, most things take up one slot (like a mace, spellbook, or small golden idol), while a handful of other items can be bundled together to conserve space (such as pitons, ball bearings, or coins), and many others require anywhere from two to four slots apiece (including platemail, a big shield, or an impressionist masterpiece). If PCs fail to eat/drink/rest they gain fatigue, which eats up inventory slots until resting for a while in a haven location (ie, not the wilderness). Inventory is cramped, basically. It's meant to be.

The d6 encounter die concept comes from Necropraxis, and has been tweaked in a few places since, most notably at Meandering Banter. I have used this nifty little system for years now across nearly all games I run, regardless of setting, rules, or theme. It just works. In terms of exploration, I've modded the idea to fit my purposes using the following framework:

Adventuring Survival Conditions:

• At minimum, characters need to eat a set of rations (food and water) when taking a short rest (overnight or otherwise, at least once per day).
• Some encounter die rolls may require additional rations to be consumed, as can some monsters, traps, or other effects.
• Lack of food/water/sleep on a short rest results in fatigue, which unit-for-unit simply takes up an inventory slot, rather than being another abstracted survival condition.
• All fatigue is reset after a long rest. Short rests have no effect on fatigue.

Overland Travel & Discovery:

• Travel overland between haven points requires hexcrawling.
• Roll the encounter die 1/day while on a road or in settled lands, 2/day off the beaten track, and 3/day in truly untamed wilds. 
• You can travel +1 hex per day at the price of gaining 1d4-1 fatigue per PC.
• You can travel -1 hex per day to forage 1d4-1 rations per PC.
• There are multiple hidden locales per hex, some of which may not be encountered on first pass-through.

Daily Travel/Discovery Distances*:

• ... by road = 4 hexes in a day 
• ... over grasslands/easy terrain = 3 hexes in a day
• ... over forests/wasteland = 2 hexes in a day
• ... over mountains/extreme terrain = 1 hex in a day

*Subject to variability based on setting/realm/plane

I do very much like the short/long rest language as borrowed from 5e. In this context, a short rest is camping overnight in a secure location, such as a cave, an outcropping, a copse of trees, or anywhere reasonably defensible within the wilderness. The encounter die is rolled once per night. PCs may regain d6+3 HP during an uninterrupted short rest.

A long rest is only available in a haven location, which is anywhere reasonably secure without the PCs having to manage the security. This would be your town/port/city/fortress. Spending a week or more in a haven location constitutes a long rest, fully restoring all HP to each PC, and relieving all fatigue.

Taking a rest of either kind in a dungeon is fundamentally impossible, barring extreme one-off circumstances.