In a regular Space Marine force, there is usually a unit or two that can almost be classified as "CC-specialists" ... Assault Marines for example. Whether you play a shooty army, a fast attack army or a Drop Pod army, the charging unit exists there for a reason.
Usually, it's to protect your shooty units from getting completely hacked up in close combat. A squad of Assault Marines followed by a Chaplain will more often than not suffice for counter-charge, but what if you want to assault with your force? How do you kit out your Tactical Squad if you want to hack apart your opponent in close combat?
First, let's take a look at the Marine stat line. It is actually pretty good for close combat. They have a good WS, S, T, I and Sv, which makes for a pretty hard-hitting unit ... but above all, they can last a couple of turns locked base-to-base with the enemy, unless they are equipped with Power Weapons or similar weapons.
Via the trait system, a Tactical Marine can exchange his Bolter for a Bolt Pistol and a Close Combat Weapon, netting him another attack when he reaches CC. He can also get the veteran skills Furious Charge and True Grit ... both great for close combat. Trust your Battle Brothers ... the trait that gives you True Grit ... will also give you Counter-Attack, which makes it almost impossible for your opponent to charge you without getting into contact with your Power Fist-Veteran. Cleanse and Purify could be quite good here too.
The Assaulting Tactical Marines needs a way to get into charge range. Usually, a Rhino will do this best, as Tactical Marines have no special movement, as in fleet or similar.
Let's take a look at one of the most basic set-ups:
Tactical SquadVeteran + 7 or 9 Marines
Simple squad set-up. Move up, unload at whatever close combat-specialist your opponent is sporting, and if you don't get charged in his turn, move up and either rapid fire again or charge at the closest enemy unit. The squad is situational when it comes to the subsequent turns. The first turn, the opponent specialists has to be utterly destroyed though, since letting for example Genestealers, Wyches, Harlequins or Banshees charge this squad is a bad idea all in all, unless their numbers are really thinned down.
The Veteran has to be equipped with a Power Fist ... the only exception to this rule would be if you're writing a list not intended for competitive play. The optimal choice for the Veteran is to simply give him a Power Fist and leave him like that. No odd shields, Purity Seals, Plasma Pistols (big no) or Auspexes.
The special weapon is up to you. The Plasma Gun will net more damage on the jump from the Rhino, and the Meltagun can be fired before an assault in a later turn. Furthermore, Frag grenades exists for a reason. You must have them to be able to kill units stuck in cover without losing numbers before you get to strike. They are worth their weight in gold.
The Rhino must be equipped with Extra Armour and Smoke Launchers. I can't stress this enough. If you fail to do this with every Rhino in your army, you'll eventually end up with Marines stuck halfway up the table, entangled in the smoking wreck of their Rhino and the squad is reduced to mere sitting ducks.
You could swap the Bolter/CCW for Bolt Pistol/CCW if you're aiming at assaulting and not letting your opponent assault. You will have an equal number of attacks if he charges you, but an extra attack per model if you get the charge. The difference lies in the number of shots on the jump. This could make a big difference if you get assaulted the turn after the jump. Wyches and Stealers will fear 8-10 Bolter-wielding Marines, but 8-10 Bolt Pistol-Marines aren't quite as scary.
The only edge the Bolt Pistol/Close Combat Weapon combinations really has above the Bolter/Close Combat Weapon is that it is cheaper ... as the first combination is free.
Furthermore, the Rhino can be swapped out for Infiltrate via See But don't be Seen, another member of the "good traits" group. If you do chose to use this, be wary that it will cut into your model count if you intend to use the Bolter/Close Combat Weapon combo on your Marines. A basic Marine with Bolter, Close Combat Weapon, True Grit, Counter-Attack, Infiltrate and Frags will cost 22 points, and that's before any Special Weapons are added. Expect a squad of those to cost somewhere 200-220 points for 8 of them, which is rather expensive.
They do make for a cool force though.
So with the bulk of the assaulting force consisting of 3 or 4 Tactical Squads either in Rhinos or with Infiltrate, and geared towards close combat, we need something to back up the Marines. Assault Marines are excellent when you have Rhinos to shield them as they move up the table. That also means that you've got a trait slot left, which means you can take Blessed be the Warriors. Blessed be the Warriors allows you to take Assault Squads as Elites, and it gives them Furious Charge ... very nice. It also frees up space from the Fast Attack slots for the second most important support unit in the force: Land Speeders. Tornados are as always better than the rest of them, with Typhoons and Multi-Melta Speeders being at least mediocre. Top it off with a good character ... say a Chaplain with a Jump Pack to follow one of the Assault Squads, and maybe a Whirlwind or two for some artillery support and you've got a viable army at around 1750 points.
There is of course a lot of other ways to equip your Tactical Squads for close combat. Regard this article as more of a set of guidelines than anything else ... bar the fact that the Veteran needs a Power Fist. That is a rule.