Buy something recognizable, buy silver. Invest smaller amounts regularly, buy silver. 1964 and earlier US coins (dime, quarter, 50 cent piece, dollar) are with limited exception 90% silver. A silver dollar has the same amount of silver in it as 10 dimes or 4 quarters or two fifty cent pieces. Of 1964 and earlier, $1,000 face value in U.S. coins contained 720 ounces of silver.
You can do the math, but I would price the coin value at what I'm paying on or around bullion price. At bullion price, a 1964 and earlier coin is worth a face value multiple determined by mulitplying 0.72 per ounce bullion price. For instance, at $10/ounce of silver the multiple is 0.72 x 10 equals 7.2; then for a dime it's silver is worth 72 cents, for a silver dollar it has silver worth $7.20 in it, and so on.
Everyone recognizes old US coins. Bring a gold piece in and who can be sure it is what you say it is...who is going to assay it, where, how quickly, etc. etc., because that is a lot of value to lose for something that is not gold and traded as gold. Also, where are you going to get change for a large piece of gold when you buy groceries and such? If a currency collapses...wait a couple of months and everyone will begin to realize there is value in silver and gold....don't squander it early if you have it.
Also, other currencies in the past (see Europe, South America, etc.) that have been inflated in the past all get called in for a new currency...mostly with a reverse value. For instance, after WWII in Austria (I think) the government announced on a Monday or Tuesday that each man, woman and child could redeem 1,200 old marks 10:1 for 120 new marks on Thursday at the bank...so on Thursday only, at banks only, each person could redeem up to the maximum of 1,200 old marks for the 120 new marks (printed on one side) and the old marks were worthless at midnight. Had a million marks in the bank you say....too bad, 1,200 for 120 per person only. A sneaky way to tax you, eh?
Also...coins are usually not affected and go over at par...that is 1 mark of coins then was worth the new mark the next day, it escaped the devaluation. Coins are too expensive to collect and remake...paper money and numbers in accounts are another thing all together. And, besides, the % of total currency and value out there was a very small % in coinage and made no difference. Point being made...save your change.
So, if you are concerned about the US currency and economic future in the light of a potential collapse, then this may be helpful information for you. If you think acquiring precious metals are foolishness, then I'm OK with that too...to each his own.