A lot of RPG players fall into the trap of thinking that they are limited to what's strictly on their character sheet. In tabletop games you are not so limited. Here are some suggested dirty tricks to get your imagination started.
Use Litmus powder, a medieval period accurate pH indicator, to tell if a pit is acidic or basic. For a simpler test, iron, lead and zinc will dissolve or corrode in acids.
Collapse the cave/ceiling in on the enemy.
Smoke the enemies out of the cave.
Spread flour around to locate invisible enemies.
Hire syphilitic prostitutes to spread disease among the soldiers in the enemy camp.
Use a small steel mirror to look around corners.
Call the Cops/Guards on the criminals/cultists/gargoyles.
Spread rats in the enemies' food supply.
Pollute the enemies' water supply with shit/rotting meat/poison.
Imitate the cry of a dangerous monster (perhasp an owlbear) to scare people.
Secret weaponry is always good. It is probably easiest to treat most of these as monk weapons.
The haughty lady's scarf and hat actually have secret blades woven into them!
The errant school boy's shoe laces are actually a garrote made out of fishing line!
The farmer's farming tool is actually a kunai that can be used as a knife and his millstone handle is actually a tonfa!
The old man's cane is actually a sword-cane!
The thug has a knife hidden in his boot!
The little girl's bracelet conceals a knife!
The peasant lady's necklace conceals a hidden blade!
The priest's holy amulet has a lead weight inside and a steel chain so it can be used like a flail!
There are lots of tricks you can perform in combat:
You don't need to use your hands to shove and trip people. You can do that using your long reaching polearm.
Throw sand into the eyes of your enemy.
Take a precisely aimed shot with a bow to pierce the enemy's cape and pin it to the ground.
Use a sling to launch Acid/Alchemist's Fire/Holy Water farther than you could normally throw it.
Smear the blade of your sword in filth such as excrement, rotting meat and poison.
Stuff your poor peasant clothing with straw padding to defend against blows (in D&D I'd rule that as padded armor and give 11 + Dex AC.)
Use natural animals as traps. Finding snakes, scorpions and wasp nests and hiding them in reed baskets that can be thrown like bombs should be a simple enough Animal Handling check.
Use firecrackers and smoke bombs to deafen, confuse and disorient enemies (especially spellcasters.)
Lasso an enemy with a rope and then pull them to the ground.
Throw a bag of glass shards in a person's face.
Drop a bag of marbles on the floor.
Booby traps are always nice. Lookup real and historical booby traps such as used in the Vietcong war. Also, remember to smear filth on your traps. Some good and simple ones:
a rope or thin cord strung across an area designed to trip people running through.
a rope or thin cord strung across an area designed to garrote people running through.
Trou de loup: A 2m diameter and 2m deep conical pit is dug. A sharp stick is hammered into the bottom of the pit. Conceal the pit with a light layer of wicker and some soil.
Caltrops are always useful.
Hang fish hooks on thin lines to eye height from high surfaces and trees.
Bamboo whip: Tie a piece of bamboo with spikes on the end back with a trip wire.
If weight restrictions are enforced in your game then they can become infuriating quickly. There are a number of ways to reduce the weight you carry.
Carry a wire saw (a wirey blade strung between two grippable handles) for a portable and light saw.
Silk ropes are lighter than hemp ropes.
Glass/obsidian knifes and tools are lighter than steel ones although they break easily.
A hammock can be simpler and cheaper than a mattress or a rug but is not usable without things to tie it up against.
There are several useful measuring devices. Note that the GM may force you to adventure and seek out wizards, elves, dwarfs and other learned creatures to find these tools or techniques.
For example, suppose one finds a strange magical liquid.
One can test the liquid's pH using a strip of litmus paper. One can test the liquid using a redox indicator.
One can then test it by measuring its density with a hydrometer.
One can measure volume using a graduated cylinder and mass with a scale and set of weights.
One can then measure its heat with a thermometer.
One can use a bolometer to see if it is giving off any sort of radiation.
A compass can be used to check magnetic properties.
A U-tube viscometer (invented in the 1800s) can be used to measure how quickly the liquid falls down through a thin capillary.
Given that the liquid is acidic, basic, reductive or oxidative one can then perform acid-base and redox titrations to determine the titration curves, acid disassociation constants and reaction potentials.
Navigation and land surveying tools and techniques can be useful for adventurers. Note that the GM may force you to adventure and seek out wizards, elves, dwarfs and other learned creatures to find these tools or techniques.
Astronomy is useful for navigation.
Know that it is noon (12 pm) when shadows point true north.
By simple clapping and time measurement the distance between two points can be calculated using the speed of sound in air (approximately 343.2 metres per second.)
There are several useful tools one can obtain: