[Exolent[jNr]]

1.

#define SECONDARY_WEAPONS_BIT_SUM ((2<<CSW_P228)|(2<<CSW_ELITE)|(2<<CSW_FIVESEVEN)|(CSW_USP)|(1<<CSW_GLOCK18)|(1<<CSW_DEAGLE)) 

This bit sum is not necessary. Just use:
if( !(PRIMARY_WEAPONS_BIT_SUM & weapon) )


2.

stock primary_wpn_drop(index)
{
    new weapons[32], num
    get_user_weapons(index, weapons, num)
    
    for (new i = 0; i < num; i++) 
    {
        if (PRIMARY_WEAPONS_BIT_SUM & (1<<weapons[i]))
        {
            static wname[32]
            get_weaponname(weapons[i], wname, sizeof wname - 1)
            
            engclient_cmd(index, "drop", wname)
        }
    }
}

stock secondary_wpn_drop(index)
{
    new weapons[32], num
    get_user_weapons(index, weapons, num)
    
    for (new i = 0; i < num; i++)
    {
        if (!(PRIMARY_WEAPONS_BIT_SUM & (1<<weapons[i])))
        {
            static wname[32]
            get_weaponname(weapons[i], wname, sizeof wname - 1)
            
            engclient_cmd(index, "drop", wname)
        }
    }
}

Don't re-index arrays.

stock primary_wpn_drop(index)
{
    new weapons[32], num
    get_user_weapons(index, weapons, num)
    new weapon;
    for (new i = 0; i < num; i++) 
    {
        weapon = weapons[i];
        if (PRIMARY_WEAPONS_BIT_SUM & (1<<weapon))
        {
            static wname[32]
            get_weaponname(weapon, wname, sizeof wname - 1)
            
            engclient_cmd(index, "drop", wname)
        }
    }
}

stock secondary_wpn_drop(index)
{
    new weapons[32], num
    get_user_weapons(index, weapons, num)
    new weapon;
    for (new i = 0; i < num; i++)
    {
        weapon = weapons[i];
        if (!(PRIMARY_WEAPONS_BIT_SUM & (1<<weapon)))
        {
            static wname[32]
            get_weaponname(weapon, wname, sizeof wname - 1)
            
            engclient_cmd(index, "drop", wname)
        }
    }
}

3.

stock fm_set_user_money(index, money, flash=1)
{
    set_pdata_int(index, OFFSET_MONEY, money, OFFSET_LINUX);

    message_begin(MSG_ONE, get_user_msgid("Money"), {0,0,0}, index)
    write_long(money);
    write_byte(flash);
    message_end();
}

Place get_user_msgid("Money") in plugin_init() and store the value in a global variable.

new g_msgid_Money;

public plugin_init()
{
    g_msgid_Money = get_user_msgid("Money");
}

stock fm_set_user_money(index, money, flash=1)
{
    set_pdata_int(index, OFFSET_MONEY, money, OFFSET_LINUX);

    message_begin(MSG_ONE, g_msgid_Money, {0,0,0}, index)
    write_long(money);
    write_byte(flash);
    message_end();
}