Well, if we're going mecha here, i've a couple weapon and support systems to consider, both for human HPAs and alien mechs.
Human
GUA 65 30mm autocannon
Basically an up scaled battle rifle carried and operated by HPA "hands". Uses banana clips for flexibility; being able to switch out, say, HE ammo to SABOT easily would be a boon in battle.
M25 automatic gattling.
Another hand carried one, this one using either normal rifle ammo or .50 slugs. Very high rpm.
"Angel Wings" Grenade Bombardment System
An array of six belt fed 25mm grenade launchers mounted on the shoulders. Inactive, they splay out and back like an angel's wings. When activated, the grenades swing up and foward, let loose a volley, then swing back down to inactive position.
Magnetic shield
This requires research. An advanced electromagnet system creates a fluctuating field extending out to a meter. Plasma weapons diffuse upon entering the field and other weapons have bullet trajectories randomly warped going inside, through, or out of the field. The HPA is temporary shut down during shielding.
Both
CQC program
Available to both HPA and alien mechs from the get-go. It's a program that, when activated, allows the mech to use it's limbs and legs as a weapon system.
Plasma lance/ monomocular swords
Upgrades to the CQC program. Plasma lances(arm mounted bars of plasma) or monomolecular swords( up scaled arm mounted monomolecular knifes) are incorporated into the program.
Alien
Plasma cannon
A up scaled plasma rifle mounted on the arm. Probably has splash damage.
AM rocket pod.
A pod of down scaled antimatter missiles also mounted on the arm. Devastating against UVGs.
"Bleeding Devil" Personal Defence System
The mech floods an area around it with plasma, dealing plasma damage to all in the vicinity.
Jumppack
Antimatter from the engine is briefly rerouted to a rocket on the back, causing the mech to "jump" over obstacles. Uses up all the remaining TUs.
Of cross maybe some people may want to switch around the weapons on both sides.