Before you make any modifications to your rifle -- learn the rifle! Get comfortable with it and with every aspect of its operation and maintenance. You may well decide that you don't need or want any modifications at all.

Of all the possible modifications -- and Lord knows they are plentiful -- the one that, to me, represents the best return for the expense is trigger improvement. There are many possible alternatives for achieving this, from a simple replacement grip bolt that allows you to adjust most of the creep our of the trigger to a replacement trigger worthy of benchrest target competition, with prices ranging from $15 to over $200. Whichever route you take, you will be amazed at how much more "user friendly" a decent trigger will make your rifle.

As for optics, really fine scopes begin at around $150 (Nikons are great), but if you use your rifle mostly for plinking or casual target work you can get by with less-expensive ones and never miss the advantages a higher-priced scope can give you (mainly, durability under rough use).

Beware of adding things just for the "cool factor" that sucks so many folks in. They tend to be expensive and may in some cases actually degrade the usability of the rifle (mainly by adding weight in return for zero performance improvement).

And magazines -- get a few. Excellent-quality mags are plentiful and inexpensive, available from many sources.

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Pisgah