Prefer a hybrid of slot-based, only tracking big items, and some general GM hand-waving (i.e. not used).
Specifically, I want the encumbrance system to broadly get characters in the ball park of "reasonable" as simply as possible, while providing a framework for GM adjudication for the outliers.
With that in mind, I make the default range and expectations somewhat generous, to encourage players to stay safely there. That's the carrot. Then the stick is that hitting "encumbered" is brutal, and only to be done when really necessary (e.g. haul unconscious party members around, or pull that heavy treasure out of the dungeon). Then then "lack of carrot" is being lightly encumbered is mainly about overland travel and/or fleeing, not tactical, every adventure play. Bottom line is that everyone sits safely in the middle and it doesn't impinge on regular play, but running out of arrows or food is still a mild concern, that can turn serious quick in some circumstances, without me having to make an ad hoc ruling on resources every time that happens.
So go in to the adventure medium encumbered. Come out medium encumbered. Since the base rules assume that, no mods to tactical movement rates or getting tired on anything else. If it all turns pear-shaped, start slinging bodies on back and hope it works out or drop gear and flee like crazy, and then get out of that state as soon as possible.